I upgraded to Firefox 3.5 about a week ago.  To be honest I have been unimpressed.  I am sure that somehow there is better protection under the hood.  Perhaps even a slight speed increase.  However, I have found more problems than obvious cures.

1. Upon opening it freezes if having trouble loading the home page for some reason.  The standard “X” in the corner is unresponsive along with the normal top menu. Leaving no choice but to force quit the application and relaunch.  It used to crash and relaunch itself at least.
2. Firefox will sometimes hesitate and freeze while opening a new tab.  For instance, I have three tabs running and click a link to open in a new tab.  Generally, I keep reading the prior open tab’s article while the new tab finishes loading.  On occasion my current tab freezes not allowing me to scroll down.  It stays frozen until the other tab finishes rendering.  Not all of the time, just part of the time.
3. Most recently it started to runaway with the processor.  I had one tab open on a very basic text only page.  There was nothing trying to auto-refresh on the page.  And yet it ran away with 80% of both cores.  Yikes.  Something in there went horribly wrong.  Once again a force quit and relaunch.

So as a whole, every day I eagerly await an update to this update.  Granted I am still a fan, just a bit frustrated not unlike when portions of my favorite highway go under construction.  I’ll be patient, but please hurry.