Call it a state of mind !
Back in Dec-2006, I'd written about my problems with Firefox. However, I just couldn't convince myself to stay with IE as my default browser for a long time (Internet Explorer Unsafe for 284 Days in 2006).
Have switched back to Firefox. Did a complete uninstall, wiped out install directories, nuked the profile directories. Reinstall has worked like a charm. No more 100% CPU utilization/freeze problems, albeit it will still be a nasty memory hog. This time, I'm making it a point not to go firefox extension crazy :)
I must admit that I didn't do proper debugging earlier. While I did do a complete uninstall, deleted installation directories, I didn't bother about the profile directory. Guess that's where the problem was (what/why it was, I don't know).
Glad to have a "normal life" now :)