Firefox crashes after upgrade to Lucid

While working on this problem, you should install a different web browser, so that you can consult Launchpad.net and other sources. Having the Mozilla.org version of Firefox installed would complicate the process of fixing this problem. So install another browser (such as Google Chromium, which is provided by the package chromium-browser), and remove the Mozilla.org version of Firefox. If you don't know how to remove the Mozilla.org version of Firefox, look for instructions on the Mozilla.org website. If you still have trouble, please post again and I'll help you with that.

Then open a Terminal window (Applications > Accessories > Terminal), paste or type in this command, and press enter to run it:

firefox

That may show some useful messages for figuring out your problem. Then run:

mv ~/.mozilla ~/.mozilla.old

Then try running Firefox again:

firefox

If that succeeds, go ahead and quit Firefox (since this running instance of Firefox would depend on the Terminal window that created it). Then you can run Firefox normally (e.g. by selecting it from your menus or clicking on a launcher for it). This technique moved out all your Firefox bookmarks, cache, and settings, so you've started fresh. If you want to try to restore them, please post again, indicating which things you want to restore. For example, if you just want to restore your bookmarks, that's easier than restoring everything.

If that doesn't succeed, please run this additional command:

apt-cache policy firefox\*

It is expected that this command will produce a lot of output. Then select all the text from the Terminal (Edit > Select All), copy it to the clipboard (Edit > Copy), and paste it here (Ctrl+V in the text box at https://answers.launchpad.net/ubuntu/+source/firefox-3.5/+question/144894 or in your email). If the above commands didn't work, then that information will enable us to figure out what we need to do next.