Dang it Jonbo298 .... so close
For extensions:
http://update.mozilla.org/
http://extensionroom.mozdev.org/
http://texturizer.net/firefox/extensions/
Extension mirror(alternate mirror)
For themes: You will need to update to new theme for Fx0.9 though a work around is possible foe testing themes not setup for theme manager)
http://update.mozilla.org/
http://texturizer.net/firefox/themes/
When installing new builds (especially release to release) DO NOT install over previous build otherwise you may encounter unwanted bugs. Back up profile (including bookmarks etc) in case.
There are several old extensions that still work fine in latest builds including Fx0.9 (ex: Nuke Anything) ,but thanks to the new manager they won't show up unless they were updated for it. So there is a handy new extension called Show Old Extensions "SOE" that allow the old extensions to be used in the new manager.
http://www.pikey.me.uk/mozilla/?extension=soe
This Firefox 0.9 release was more for new features and such, so branch builds (based on mozilla 1.7 branch) now to next release is primarly BUG fixing so next release should be best version yet hopefully.
http://www.mozilla.org/projects/firefox/roadmap.html