Firefox Meltdown

So I fire up the computer this morning and click the Firefox button.

Wait

Wait some more

Open a terminal window, give the command
$ ps xawu | grep -i fire

nothing running.

Type firefox in the terminal window. Get back a prompt. $ echo status yields 255. This is Not Good. (You want to see a 0 here.) OTOH, at least I know something's wrong with Firefox, not some weird thing with the window manager or something else that's been updated.

Try again:

$ firefox http://cst-www.nrl.navy.mil
INTERNAL ERROR on Browser End: Expected a version > 5! Version = 4

System error?:: No such file or directory
$ echo $status
255
$

Very bad. No idea what it means. What to do? Panic seems a good option, but let's assume that it's not Firefox that's corrupted, rather something in my Firefox preferences, extensions, or whatnot. So try:

$ cd ~
$ mv .mozilla .mozilla_old
$ firefox

And wonder of wonders, Firefox runs. Of course, now I have to copy my bookmarks from ~/.mozilla_old to ~/.mozilla, and reinstall the extensions, but at least it's running.

It's possible to do things like this in Windows, but I find it much easier to figure out the local settings of a program under Unix -like operating systems. Of course, I don't know what went wrong here, but at least I got things back to work quickly.