User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:10.0.2) Gecko/20100101 Firefox/10.0.2 Build ID: 20120215223356 Steps to reproduce: it seems that, despite falsifying all the previewing preferences in about:config, firefox keeps trying to create the taskbartabpreview. Please have a look at this crash report: https://crash-stats.mozilla.com/report/index/bp-7f39e493-9401-49c7-a6bd-0086b2120222 In this case i ran firefox in an embedded setup, and i got the assertion "Cannot use taskbar previews in an embedded context" , even if i disabled taskbar previews everywhere. a brutal solution that solved the problem was to make the function WinTaskbar::CreateTaskbarTabPreview() (WinTaskbar.cpp, ln 403) return always NS_OK. Please honor the taskbar previewing preferences in the next releases :)
I think we should just early-return out of http://mxr.mozilla.org/mozilla-central/source/browser/modules/WindowsPreviewPerTab.jsm#463 if AeroPeek.enabled is false.