I began migrating my Firefox extensions from Windows to Ubuntu by installing Extension List Dumper in Windows’ Firefox, and then working my way through the list generated by it in Ubuntu. However, at some point I discovered that Stylish‘s userstyles were no longer being applied, and that Firefox could no longer restart itself using the Restart button which becomes available after installing an extension.
What’s worse, using the command-line to start Firefox I discovered that it did attempt to restart when told to, but it only resulted in a Segmentation fault.
I initially suspected that there was some sort of a conflict between the beautiful NASA Night Launch theme and Stylish, but after starting with a new, clean profile and installing extensions one by one instead of en masse, I finally traced the problem back to Colorzilla, one of my favorite extensions. Without it, everything seems to be working, and with it, Firefox segfaults two, sometimes three times in a row before finally restarting. So the workaround to the problems listed in the title is to uninstall Colorzilla.
The problematic version of Colorzilla I was using was the one currently available from Mozilla’s Add-ons page, 1.0. A new Beta version is available from Colorzilla’s official home page, which also mentions problems with Ubuntu and FC5, and suggests a solution which, if it works, should allow you to keep using the non-Beta version of Colorzilla. I haven’t tested either of these solutions.
I haven’t come across these issues with Colorzilla under Windows.
When tracking down this problem, the Restart Firefox extension turned out to be quite handy.