Description of problem:

In the Extension catalog, when an extension provides no icon, a grey box is shown, which may be confused for a skeleton loader.

Prerequisites (if any, like setup, operators/versions):

Steps to Reproduce

1. Add marketplace Plugin yaml without an icon

Actual results:

When an extension provides no icon, a grey box is shown, which may be confused for a skeleton loader.

Expected results:

A nicer placeholder is given Figma

Reproducibility (Always/Intermittent/Only Once):

Always

Build Details:

Additional info (Such as Logs, Screenshots, etc):

1. 1.5 test day
2. Firefox 136.0-2.fc41