Brain on Fire Tim McCormack, distilled.

Problem: Firefox on Ubuntu is crashing when it encounters flash content. Solution: Uninstall the libflash0c2 package.

This post contained incorrect information and has been modified.

Problem

Ubuntu (Hoary Hedgehog) wanted to upgrade Firefox from version 1.0.6 to version 1.0.7, but the upgrade barfed with errors like this: dpkg: error processing /var/cache/apt/archives/mozilla-firefox_1.0.6-0ubuntu0.1_i386.deb (--unpack): trying to overwrite `/var/lib/mozilla-firefox/extensions.d/00classic', which is also in package firefox dpkg-deb: subprocess paste killed by signal (Broken pipe) After that, firefox would no longer start. Apparantly, I somehow had both the "firefox" package and the "mozilla-firefox" package installed. Additionally, they seemed to have cross-dependencies, and simply uninstalling firefox would also affect the packages "yelp", "ubuntu-desktop", and "language-support-en".

Solution

1. Remove all firefox packages. In System:Administration:Synaptic Package Manager, do a search for "firefox" and mark all packages there for removal. Click the "Apply" button, and make note of any other packages that will also be removed. On my system, they were "yelp", "ubuntu-desktop", and "language-support-en".
2. Reinstall Firefox. In the package manager, mark "firefox" for installation, along with "firefox-dom-inspector" (optional, but I recommend it) and "firefox-gnome-support". If you use a non-US locale, reinstall that as well (it will be something like mozilla-firefox-locale-xx). Apply changes. You should now have the latest version of Firefox, and it should be functional.
3. Reinstall the affected dependent packages. Search for and install those dependent packages you wrote down two steps ago. Your system should now be essentially unchanged, other than the Firefox upgrade. In the future, only the "firefox" will need upgrading -- this is a one-time bug.

Explanation

When the Firefox project split off of Mozilla, there was some trickiness in the package naming. The result is a legacy package (mozilla-firefox) that interferes with upgrades -- they share files. Once you kill both and reinstall one, there's no conflict. Incidentally, as long as your settings are stored in the default location, they should carry over to the new install. Make sure to use "Mark for removal", not "Mark for complete removal"; the latter destroys your settings.

Resources

Original solution in an Ubuntu support thread.

I discovered an interesting bug in Firefox today. While working up a layout for a new design, I created a directory with the design version number in it, "1.5". Upon viewing the page in Firefox, I discovered that the relatively linked stylesheet was not being applied. Amazingly it worked as expected in IE. (Well, except for the box model, and the margin:auto, etc.) I half-heartedly searched google and del.icio.us for similar issues. I reinstalled firefox and disabled some extensions. I did a virus scan (some other programs had been acting up). No dice.

And then I did what I should have done in the first place: I blamed myself, not the program -- and replaced the period with an underscore. Everything works fine now. Except IE, needless to say.