3.6 was a while ago, and I believe you didn't need add-ons to have the trouble you describe.
I use Firefox and Chrome every day. My results line up with recent HN comments about how Firefox is competitive, uses less memory at scale (lots of tabs), still janks worse, but may be actually more stable at the moment. Flash is a big source of instability still, for both browsers.
My bottom line: both Firefox and Chrome are competitive, leading-edge browsers. Firefox on desktops is pure open source, Chrome is not (if that matters to you; it does to me a bit, but I'm a realist). AwesomeBar wins for me over Omnibox.
You are far from the first Mozilla employee that has responded to my complaints about Firefox, but you are the only one thus far that has been civil. In fact, just a few days ago, I was trolled on twitter by a Mozilla employee over my responses here.
Sorry to hear about the trollery. I'm looking into it.
I wonder if you have a profile that goes back years and has some property that tickles a latent bug. Sorry if I missed it: have you tried running on a brand new profile? You'll have to use the -ProfileManager option on the command line at startup, I think.