Open an application in BrowserSim. Right-click simulated device and click debug>firebug lite. When firebug lite window opens, part of the test is obscured behind 'html'.

Clicking through 'console', 'html', 'css' etc. buttons causes the text to become obscured and unobscured repeatedly. In one instance multiple clicking seemed to resolve the problem.

This is perhaps an upstream issue but reporting here as a first port of call.