Upgraded to 5.0: seems faster starting up and loading pages, but it disabled a bunch of add-ons, even more than usual for Firefox upgrades. Compatible add-on versions usually, but not always are available later.
Will have to see how it holds up after several hours of browsing.
Looks like they did the same thing IE9 did. add-ons give them a bad name so they disabled them and make it easier to kill them.
It’s like this. My browser is slow. The vendors found out it was add-ons making it slow so they disable them. Hey my browser is fast now. Oh wait, I’m missing my 100 add-ons. Let me turn those on. Hey my browser is slow. Damn browser sucks.