Another idea being "copied" (or maybe not) from Chrome.

Lorentz is meant to isolate plugins into separate processes so that if it crashes, it doesn't bring down the whole browser, and will restart crashed plugins.
I think it only does Flash, Silverlight and QuickTime right now.

Personally, am unsure about the effects on speed and memory of this - I doubt there'll be much of an improvement here.
However, maybe it'll lead to the ability to install new plugins without having to restart the browser...

More info here:
http://eming.com/en/firefox-lorentz-keep...r-control/