This past week, my Firefox has begun to slow to a crawl after about 1 hour of usage. When this happens, I cannot get the bookmarks to open up (or at least pulling up that menu is very slow) and I have to go to Task Manager to shut it down. I don't know if it's an update to Firefox itself that is causing this or if it was an update to an extension.
You're not alone, I have it on three PCs and it got so bad on all three that I have switched to Chrome for good even though Chrome is still Beta and is not a full blown app yet (very poor print support). But its good enough for casual browsing and 10x faster than FF with almost no crashes (FF crashed after 2-3 hours of use for me, but I had it retain 999 days of history data).
If you want to stick with FF, try to minimize the amount of history data stored in form of history/cookies/passwords and see if that improves performance. FF keeps all that data in a database. It begins to hog the system once that DB get big.
Also, try the following if you believe you have a large history DB (this will defragment it and improve its performance)
- Open the Error Console: Tools menu/Error Console
- In the Code text box paste this (it's a single line): Components.classes["@mozilla.org/browser/nav-history-service;1"].getService(Components.interfaces.nsPIPlacesDatabase).DBConnection.executeSimpleSQL("VACUUM");
-Press Evaluate. All the UI will freeze for a few seconds while databases are VACUUMed