I had, naively, installed Firefox using the installer that’s available on their site. Naively because I had done this in /usr/local/firefox, a generally accessible directory, for those not quite aware of how unix works. This works fine for most purposes. The one thing that just didn’t seem to work as intended was installing/uninstalling extensions and for the longest time I couldn’t make sense of it.
Today Josh and I were brainstorming about this, triggered by his blog entry about a Firefox extension, where he mentions he doesn’t have a Linux machine available for testing. Well, I do, but I couldn’t get it to work, or any other extensions for that matter, so… first of all we tried to eliminate all external influences, by means of uninstalling the other extensions. Oddly enough that didn’t work. Removing all sorts of application directories in my home-directory also didn’t work. With the namechanges that Firefox has had in the past there were a few: ~/.firefox, ~/.mozilla-firebird, ~/.mozilla, ~/.phoenix. Hrm. Finally the thought occured to (one of) us that perhaps Firefox was trying to write to a file in /usr/local/firefox, which wasn’t going to work because those files and directories under there are readonly for a regular user and can only be modified by the system administrator.
Time for a *lightbulb moment* here. Was that Firefox installer really intended to be installed in someone’s home-directory, not in a system directory? Gah, what a thought! I’m so used to installing applications system-wide on my computers that the idea of (compiling and) installing something in my home-directory only never occured to me! Two minutes later I’d installed an additional copy in my home-directory and sure enough, everything works fine now.
With that sorted, I can confirm that Josh’s extension works fine under Linux as well. 
Another extension that I finally got around to try now, also works like a charm and might just convince me to switch to Firefox all the way, dropping Opera. That would be the Session Saver which allows me to crash and burn and happily resume browsing afterwards, having restored all Firefox windows and tabs, including their history. Admittedly I’ve only tested it for a short while but it looks promising. Time to load a load of pages into Firefox windows/tabs and see what happens. 
Here’s the only major drawback I’ve found with sessionsaver — repeatable crashes are a problem. For example, if I open chrome://browser/content/ in a tab, rather than a new window, my browser crashes when I try to close that tab (I don’t know if this crash is cross-platform). No problem, sessionsaver gives me my tabs back — including the chrome tab that kills the browser when I try to get rid of it.
A more annoying example would be…any plugin-using page that exposes a crash in said plugin. Launch firefox, and it autoloads the crashing page on you. Sometimes, I’m afraid, you just have to find and edit your prefs.js to fix things.
True, but there is that same drawback with Opera’s behaviour. On startup you can choose to start from where you left off (be it an auto-save or where you explicitely exited the browser) or with an empty browser. Nothing inbetween, nothing like prompt me for every single tab, alas, and I can’t imagine noone has ever suggested that idea to the developers before, so I’m guessing it’s not a high priority or they just don’t care enough.