This epic will track the work that is required to rebase Firefox ESR packages in RHEL from version 115 to 128. For the common information (i.e. schedule) about Firefox ESR and Thunderbird rebases see the parent feature - RHELBU-2535. Process related tasks are tracked in DESKTOP-821.

Summarized changelog - for more information please look at https://en.wikipedia.org/wiki/Firefox_version_history#Firefox_115_through_127 and changelog for 128 release itself:

• Firefox 116 was released on August 1, 2023. Major changes included the sidebar switcher allowing users to access Bookmarks, History and Synced Tabs panels easily, quickly switch between them, move the sidebar to another side of the browser window, or close the sidebar; available access to the release notes in the update notification prompt in the form of a "Learn More" link whenever an update is available in English locales; the ability for users to copy any file from their operating system and paste it into the browser; the volume slider in Picture-in-Picture; the possibility to edit existing text annotations; the improvement of the upload performance of HTTP/2 on those with a higher bandwidth delay product; added support for the dirname attribute to pass text directionality information about input and textarea elements to the server; added support for CSP3 external hashes; the Audio Output Devices API that now enables sites to redirect audio from media elements to permitted output devices (speakers) other than the system default for the user-agent; added upport for proper BYOB readers on Fetch and WebTransport, which allows developers to prepare their ArrayBuffer so that it can be reused for read requests and thus saves memory allocation.

• Firefox 117 was released on August 29, 2023. Major changes included the extension of support for credit card autofill to users running the browser in the IT, ES, AT, BE, and PL locales; the addition of a dom.event.contextmenu.shift_suppresses_event preference to prevent the context menu from appearing; the browser no longer showing its own screen sharing indicator on Wayland desktop environments; the enhancement of web compatibility inspection with the new CSS compatibility tooltip in the Developer Tools Inspector; added support for improved CSS nesting by default; support for RTCRtpScriptTransform, ReadableStream.from (allowing creation of a ReadableStream from an (async) iterable), and the math-style and math-depth CSS properties and the font-size: math value.

• Firefox 118 was released on September 26, 2023. Major changes included the introduction of automated translation of web content, courtesy of the EU-funded Project Bergamot; the use of the FDLIBM math library on all systems to improve anonymity with Fingerprint Protection via web audio in the browser; the restriction of visibility of website fonts to system fonts and language pack fonts to mitigate font fingerprinting in Private Browsing windows; the availability of Video Effects and background blur on Google Meet; the ability for U.S. Firefox Suggest users to see browser add-on suggestions right in the address bar based on their keywords; support for CSS math functions round, mod, rem, pow, sqrt, hypot, log, exp, abs, and sign; OpaqueResponseBlocking enabled by default.

• Firefox 119 was released on October 24, 2023. Major changes included the addition of Firefox view and the PDF editor; recently closed tabs now persisting between sessions that don't have automatic session restore enabled; the ability to import extensions from Google Chrome; support for the partitioning of Blob URLs, which mitigates a potential tracking vector that third-party agents could use to track an individual; the restriction of the visibility of website fonts to system fonts and language pack fonts in Enhanced Tracking Protection strict mode to mitigate font fingerprinting; an update to the Storage Access API to improve security while mitigating website breakages and further enabling the phase out of third-party cookies in the browser; the addition of Encrypted Client Hello (ECH), which extends the encryption used in TLS connections to cover more of the handshake and better protect sensitive fields; media sniffing no longer being applied to files served as type application/octet-stream; the inclusion of the Santali (sat) language; a fix for an issue causing unexpected jumps in scroll position on Facebook; several enhancements to the Inactive CSS styles feature, which assists in identifying CSS properties that have no effect on an element; the automatic switch to a raw data view if the JSON is invalid or broken; added support for ARIA reflection for simple attributes and default Accessibility Semantics for Custom Elements; added support for credentialless in Cross-Origin-Embedder-Policy; added CSS attr() function for a fallback parameter; easier grouping of items by using the methods Object.groupBy or Map.groupBy

• Firefox 120 was released on November 21, 2023. Major changes included added support for a new "Copy Link Without Site Tracking" feature in the context menu which ensures that copied links no longer contain tracking information; added support for a setting (in Preferences → Privacy & Security) to enable Global Privacy Control and inform websites that the user doesn't want their data to be shared or sold; the enhancement of the Canvas APIs with Fingerprinting Protection for the browser's private windows and ETP-Strict privacy configuration for the protection of users' online privacy; the enabling of Cookie Banner Blocker and URL Tracking Protection by default in private windows for all users in Germany; the import of TLS trust anchors (e.g., certificates) from the operating system root store; the addition of keyboard shortcuts for editing and deleting a selected credential on about:logins; added support for corner snapping on Windows and Linux for Picture-in-Picture; the addition of the User Activation API, which allows servers to send resource Link headers before the final HTTP response and improves performance on servers using this feature; the ability for users to use an added devtools feature to simulate browser tabs to be offline; the Style Editor panel's feature of a new "Pretty Print" button located in the footer of the panel, similar to the pretty print button found in the Debugger panel, used to format stylesheets (e.g., those that are minified); the Rules panel within the inspector panel no longer displaying colors in the new CSS Color 4 formats (e.g., OKLCH) as hexadecimal/named colors, ensuring that it matches the original values used; the ability for lh and rlh units to be parsed and computed correctly as lengths; the enabling of WebAssembly GC by default, which allows new languages, such as Dart or Kotlin, to run on the browser

• Firefox 121 was released on December 19, 2023. Major changes included a default to the Wayland compositor when available instead of XWayland for Linux users; the ability to force links to always be underlined, which can be enabled in the Browsing section of the Settings menu; the floating button in the PDF viewer to simplify deleting drawings, text, and images added in PDFs; the Firefox Debugger including a new feature: an option to disable the debugger; keyword on the current page; the unification of the focus indicator across the toolbox, which is now larger with improved contrast, featuring a white box-shadow for enhanced visibility on blue backgrounds; added support for the :has() selector, which authors to match an element that has, or "anchors", at least one element matching its relative selector; added support for the hanging and each-line keywords for the text-indent CSS property, offering more convenient paragraph layout options for styles such as bibliographies, poetry, etc.; added support for the balance keyword for the text-wrap CSS property, which can improve the appearance of short multi-line text blocks such as long headings or captions by harmonizing the line lengths; added support for the lazy loading iframes, which are only loaded when visible, so non-critical iframes can load later when needed to speed up initial page loads, reduce initial network usage, etc.; added support for tail call elimination in WebAssembly language to improve support for functional languages

• Firefox 122 was released on January 23, 2024. Major changes included new displays of images and descriptions for search suggestions when provided by the search engine; improvement in the quality of translated webpages in the translations feature; the availability of MDN Web Docs article suggestions from Firefox Suggest in the address bar for users searching for web development-related information; the line breaking rules of Web content matching the Unicode Standard, improving Web Browser compatibility for line breaking; a fix for keyboard navigation in Inspector Rules view; enabled offset-position property which is useful for most of the offset-path values; added support for ray(), basic-shape and coord-box to the offset-path CSS property; added support for rect() and xywh() basic shapes on clip-path and offset-path CSS properties; added support for animating the SVG viewBox attribute using SMIL by animations; LargestContentfulPaint API, which provides timing information about the largest image or text paint before users interact with a web page; added support for hr in select, allowing websites to easily use separators inside a select element; added support for the showpicker method on <select> elements; the fallback URL parser for unknown schemes changed to DefaultURI, improving specification adherence and web compatibility; the ArrayBuffer.prototype.transfer proposal methods, which enables transferring ownership of ArrayBuffer data; added support for the Screen Wake Lock API; recognition of the "webauthn" autocomplete token; the ability for scripts to store cacheAPI data in Private Browsing mode; the tainting of filters that use currentColor as an input to further protect user privacy; Uneven Level Protection Forward Error Correction (ULPFEC) turned on by default.

• Firefox 123 was released on February 20, 2024. Major changes included the integration of search into Firefox View, allowing the user to search through all of the tabs on each of the section subpages - Recent Browsing, Open Tabs, Recently Closed Tabs, Tabs from other devices, or History; the Web Compatibility Reporting Tool; the ability to translate text in tooltips (i.e. titles) and text displayed in form controls (i.e. placeholder) when translating web pages; the implementation of the address bar settings in the Firefox Settings' Search section; the support for the Network Monitor for saving a response body to disk through the Save Response As context menu item; the implementation of linearRGB interpolation for SVG gradients, as well as the existing sRGB interpolation; the SVG content falling back to use the default replaced element values of 300px width and 150px height and the feImage no longer failing to render; added support for Early Hints by enabling Preload and Modulepreload support; the application of audio echo cancellation to microphone inputs when the audio output is redirected to another device with setSinkId(); added support for declarative ShadowDOM, providing developers greater flexibility and improved ergonomics when working with ShadowDOMs directly within HTML; the report of ARM64 Linux's CPU architecture as "x86_64" and ARM and x86 Android's as "armv81" in the User-Agent string and the navigator.platform and navigator.oscpu Web APIs (Android); the off-main-thread canvas on macOS, Linux and Android; and various security fixes

• Firefox 124 was released on March 19, 2024. Major changes included the caret browsing mode now working in the PDF viewer; open tabs now being sorted by either recent activity (which is set by default) or tab order in Firefox View; the expansion of Qwant's availability to all languages in the France region along with Belgium, Italy, the Netherlands, Spain, and Switzerland; various security fixes; added support for AbortSignal.any; the ability to use HTTP(S) and relative URLs when creating WebSockets

• Firefox 125.0.1 was released on April 16, 2024. Major changes included added support for the AV1 codec for Encrypted Media Extensions (EME), enabling higher-quality playback from video streaming providers; added support for text highlighting for the PDF viewer; the display of pinned tabs in the Open tabs section for Firefox View; the prompt for U.S. and Canadian users to save their addresses upon submitting an address form, allowing the browser to autofill stored address information in the future; the ability to more proactively block downloads from URLs that are considered to be potentially untrustworthy; the URL Paste Suggestion feature providing a convenient way for users to quickly visit URLs copied to the clipboard in the browser address bar; the ability for users of tab-specific Container add-ons to search in the Address Bar for tabs that are open in different containers; an option to enable Web Proxy Auto-Discovery (WPAD) while configured to use system proxy settings; the tab key now only reaching the first option rather than cycling through all available options in a group of radio buttons where no option is selected, and the ability for the arrow keys to navigate between options as they do when there is a selected option, making keyboard navigation more efficient and consistent; the option to disable the Pause Debugger Overlay that appears over the page content when the debugger pauses JavaScript execution; a new drop-down menu button at the bottom of the source view in the Debugger panel, specifically designed for Source Map related actions; added support for the popover global attribute used for designating an element as a popover element; the enabling of WebAssembly multi-memory by default; added support for Unicode Text Segmentation to JavaScript; added support for contextlost and contextrestored events on HTMLCanvasElement and OffscreenCanvas to allow user code to recover from context loss with hardware accelerated 2D canvas; added support for the navigator.clipboard.readText() web API; added support for the content-box and stroke-box keywords of the transform-box CSS property; the align-content property working in block layout, allowing block direction alignment without needing a flex or grid container; removal of support for SVGAElement.text in favor of the more widely-implemented SVGAElement.textContent method; various security fixes

• Firefox 126 was released on May 14, 2024. Major changes included the Copy Without Site Tracking option that can now remove parameters from nested URLs, and includes expanded support for blocking over 300 tracking parameters from copied links, including those from major shopping websites; support for Content-encoding: zstd (zstandard compression), which is an alternative to broti and gzip compression for web content, and can provide higher compression levels for the same CPU used, or conversely lower server CPU use to get the same compression; the addiion of the Catalan language; added telemetry to create an aggregate count of searches by category to broadly inform search feature development; the temporary disabling of the URL Paste Suggestion feature while a potential performance issue was being investigated; an option to disable/enable the Developer Tools' split console feature; the implementation of URL.parse(); the enabling of the CSS zoom property by default following a lot of web compatibility and standardization work in the CSSWG; added support for CSS Custom :state() and CustomStateSet pseudo-classes; added support for Screen Wake Lock API; added support for IDBFactory.databases for enumeration of IndexedDB databases; various security fixes

• Firefox 127 was released on June 11, 2024. Major changes included setting the browser to auto-launch, which optimizes efficiency in our browser-centric digital routines, eliminating manual startup delays and facilitating immediate web access; the enabling of DNS prefetching for HTTPS documents via the rel="dns-prefetch" link hint; the Close duplicate tabs command available from the List all tabs widget in the tab bar or a tab context menu; the ability to automatically upgrade <img>, <audio>, and <video> elements from HTTP to HTTPS if they are embedded within an HTTPS page; the report of the CPU architecture for 32-bit x86 Linux as x86_64 in the User-Agent string and navigator.platform and navigator.oscpu Web APIs; support of the Screenshots feature for taking screenshots of file types like SVG, XML, and more as well as various about: pages within the browser; the screenshot tool being more accessible to everyone by implementing new keyboard shortcuts and adding theme compatibility and High Contrast Mode (HCM) support; improvement of performance for capturing large screenshots; the enabling of navigator.clipboard.read()/write(); various security fixes.

• Firefox 128 and Firefox 128 ESR were released on July 9, 2024. Major changes included the ability to translate selections of text and hyperlinked text to other languages from the context menu; the ability to show recent searches or currently trending searches when U.S. and Canadian users open the Address Bar to get them back to their previous search session or inspire the next one; a simpler and more unified dialog for clearing user data, which provides insights into the site data size corresponding to the selected time range in addition to streamlining data categories; added support for playback of protected content from streaming sites like Netflix while in Private Browsing mode; added support for the experimental Privacy Preserving Attribution API, which provides an alternative to user tracking for ad attribution; microphone capture through getUserMedia now using system-provided voice processing when applicable, the Saraiki (skr) language; the proxy of DNS by default when using SOCKS v5, avoiding leaking DNS queries to the network when using SOCKS v5 proxies; added support for rendering more text/* file types inline, rather than requiring them to be downloaded to be viewed; the renewal of the root certificate used to verify add-ons and signed content to avoid upcoming expiration; the display of CSS rules specificity in a tooltip when hovering a CSS rule selector in the Inspector Rules view; the ability for the Inspector panel to flag a custom property declaration as invalid when the value does not match the registered custom property definition; improvements to Inactive CSS displaying a warning when column-span is used on elements outside of multi-column containers and when properties only applying to replaced elements are used on non-replaced elements; added support for Resizeable ArrayBuffers and Growable SharedArrayBuffers in SpiderMonkey; the ability of the setCodecPreferences method to allow applications to disable the negotiation of specific codecs (including RTX/RED/FEC), and an application to cause a remote peer to prefer the codec that appears first in the list for sending; the change of the Accept header for images and documents to better align with the Fetch standard and other browsers; added support for @property and the CSS properties-and-values API; the provision of a new bytes() method on many objects like Request/Response and Blob that provides a convenient way of getting an Uint8Array typed array; various security fixes (both).

For even more summarized changelog between 115 and 128 take a look at https://www.mozilla.org/en-US/firefox/128.0esr/releasenotes/.