You've probably read Mitch Wagner's post extolling the virtues of the just-released Firefox 3 Beta 5.  I've had experiences that are no less grand than his, albeit with one little exception that illustrates the hazards of beta-to-beta upgrades.

First off, I haven't been using the default FF3 install -- I've been using the PortableApps.com version, which I can run side-by-side with my older FF2 setup without disturbing anything.  Beta 4 was extremely stable and fast, so I was looking forward to a beta 5 edition from the PA.com people.  Before I ran beta 5, though, I did two things that would stand me in good stead later: I made a backup copy of the beta 4 directory, and I exported my bookmarks.

The problems all centered around the bookmarks, no doubt due to the new way bookmarks are managed internally.  I have a great number of RSS feeds which are accessed from my bookmarks toolbar, but when I imported them into beta 5, they showed up as blank folders.  No feeds, no nothing.  And that wasn't the worst of it: the Unfiled Bookmarks folder, which had a lot of stuff in it, wasn't being imported properly, either.  I dreaded the idea of having to schlep all of this stuff back into beta 5 manually, but decided to try another couple of approaches first.

Since the PA edition of Firefox only keeps a single user profile (it's in the program's /data/profile directory), I decided to try copying the beta 4 profile directory into beta 5 to see what happened.  That turned out to be the magic solution: everything upgraded perfectly.  I also found, later on, that the bookmark backup/restore file format, not to be confused with the regular bookmark import/export function, now exports to a .json file, and not the usual .html.  More evidence of internal changes.

Moral of the story: Beware those dreaded beta-to-beta upgrade buglets.  But that bit of rough sea aside, it's been smooth surfing for me ever since.