I honestly wish I could use Firefox as my development environment. I prefer Firebug to the Chrome dev tools. But I've been slowly forced to admit that it can't keep up. With Chrome, I can casually open up a dozen tabs without considering the consequences; in Firefox, I get worried when I have two open. This pans out in the Activity Monitor.
There exist huge inconsistencies in all of these claims, and it's extremely strange how difficult it is to work out what third variables are involved that are causing such vastly different reports.
I have heard reports of considerable performance improvement from users clicking on "Firefox Reset" button. Have you tried it? You can find it in about:support (or somewhere in the Help menu, I can't remember where).
There exist huge inconsistencies in all of these claims, and it's extremely strange how difficult it is to work out what third variables are involved that are causing such vastly different reports.