Finally - I simply created a new Firefox profile and transferred the bookmarks, passwords, etc... that I wanted to carryover. This resolved my issues completely. So before you throw away FF4 in frustration - try creating a clean profile. Probably not a bad idea anyway - I noticed FF3.0 cruft in my profile that I shed as part of this process.
Resolving Firefox 4 issues on Mac OS X Snow Leopard
I encountered all types of strange behavior using Firefox 4 after my recent upgrade. The nastiest bug prevented me from accessing any windows other than the primary Firefox window. So all popups, while listed on the Windows menu, were completely inaccessible. I tried all the typical workarounds like disabling Addons and running in Safemode. But nothing permanently fixed the issue.