Is OSX 10.6.8 too old? Constant slow/lockup w/ FireFox, which constantly draws high %CPU rate

I switched to FireFox when Safari started to have massive problems. Firefox is not much better. Mozilla forum responses keep blaming AddOn incompatability. But mostly I'm running security & privacy enhancers (DoNotTrackMe, Ghostery, etc)

I have a DSL line.

I've got an MBP 2.66 Ghz Core i7, wish I could install more than 8 GB memory. I tried a PCI card, but it causes a kernel panic (Delkin Devices ExpressCard 34 PRO SSD PCI Express)

I want to keep >100 tabs open. Closer to 200. Used to be able to do that with Safari. What has changed ?

FF was working adequately until the last security update. Now its just constantly showing anywhere from 20% to 80+ %CPU usage. It can take many seconds to open a new blank tab, and then 10-20 seconds before it accepts input (trackpad click on the URL box, or keyboard entry).

Seems like every other FF update screws it up.