Hmm. I recently started having some crashing issues with my Firefox too, in W2K, that was rock-stable prior. I had no problems with the upgrade to a 1.0PR 2004-10-14 nightly, I upgraded my extensions, etc. I then decided to try the FlashGot extension, which I guess behaves a little different than most, since it installs an actual executable binary into the profile as a helper app. Well, I decided that the extension wasn't doing me much good, so I un-installed it. I started having crashes, and one thing that I noticed was, that the \Mozilla\Firefox\pluginreg.dat or whatever file had changed, and some settings associated with plugins listed as in a sub-directory of my Opera installation, appeated to have become "active". Even wierder, I had the same plugins listed twice, once in the Opera plugin dir, and once in the Firefox dir, and the Firefox ones were newer. So I think that somehow, by un-installing FlashGot, I cause Firefox to re-scan for plugins, and it somehow "activated" the older versions of some things like Flash from the Opera installation directory, with priority over the newer ones in my Firefox program directory.
So one thing that you could try, would be re-naming/moving \Documents and Settings\(username)\Application Data\Mozilla\Firefox\pluginreg.dat, and possibly any of the plugins that might reside in another browser's program/plugin directory, and see what happens.