Firefox 2.0.0.12
I use Firefox because for a long time I believed it was a superior and safer browser than Internet Explorer 6. And, while it is mostly stable on my Linux and Mac boxes, Firefox is a disaster on my Windows PC. It crashes, it leaks memory (very badly!), and add-ons wreak havoc on its already tenuous stability. And, oh yes, Firefox 2.0.0.11 doesn't run at all one my old iBook G4 that still runs Panther (Mac OS X 10.3). So, it was interesting to note that Mozilla calls the 2.0.0.12 release a stability e and security update. I still don't see anything about fixing memory leaks for the Windows version in the list of security fixes. Here's hope that Firefox 3.0 addresses these problems.
Firefox 1.5 would have gotten a 4 or 5 (out 5) Walruses rating back in its day. I grudgingly give Firefox 2.0 a 3 Walruses rating only because it gives me a consistent (if buggy) interface across my Windows, Mac OS X, and Linux computers.
ADDENDUM Firefox's auto-update routine works under Windows XP. However, if you are running Vista, it looks like you have to go to the Firefox.com site, download a full copy, and run a full installation to update to 2.0.0.12.
The anecdotal evidence of
The anecdotal evidence of Firefox 2's instability just isn't really prevalent out there, except of course for the memory leaking. I don't think I personally have ever had it crash except when I tried to do evil things to it like copy FLV files out of the temp directory with Unlocker.
If you go to a particular set of websites or use a particular set of add ons that cause Firefox to go unstable, I'm sure the Mozilla project would like to know about it. Here's hoping the new Gecko works better for you.
The auto-update works fine
The auto-update works fine for me on Vista.
For the security part, I don't know. The security hole related to their jar: URI scheme, they left open for 8 months, were disappointing. But I don't know any equivalent to NoScript on other browsers.