I just upgraded to FF 3.5.1
It's definitely faster now but we'll see about the memory problem.
They fixed that slow startup thing which was bugging me.
http://en-us.www.mozilla.com/en-US/f....5.1/whatsnew/
All you need to do is check for updates from the Help menu in FF.
edit
that wasn't the direct url to the changes. This one is.
http://en-us.www.mozilla.com/en-US/f.../releasenotes/