How to Make Firefox Stop Lagging and Give Script Errors

So for a while I've been using Firefox 13 without upgrading manly cause Firefox never told me about it. I upgraded to the latest version and i've been having the worst experience. Everything would lag and be so slow. I'd get the beachball every time I attempt to do anything. I tried to to down grade back down and it hasn't been the same. Same issue.

I did a lot of different things to try to fix it, and it worked, but then instead I get that Unresponsive Script Error constantly instead, and although that's not as bad, it becomes a problem when I save a file because when the script error comes up, I can't save a file. I tried to do suggestions on how to get rid of that, but when I do that it goes back to lagging hardcore again.

Does anyone have any suggestions on how to make Firefox fast again?

JediMeister said:

Do you run add-ons with Firefox 18? Have you tried disabling them and running just the stock copy? How about recreating the profile? It is strongly advised that you backup your bookmarks before doing this, unless you don't have any or don't care.

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Well since then i downgraded to Firefox 15, and that's helped a bit, and at times it will be fast, but it hasn't been the same since the good old days. I've also been hearing others with this issue do that and it doesn't help them.