This is an unbelievable trick. If you’ve been running Firefox for a long time, it gets a lot more sluggish. Here’s how to optimize its databases and give it back its youthful vigor.First, go to Tools, Error Console. Copy and paste this long and obnoxious line in:
Click Evaluate and wait. Firefox will appear to lock up, but fear not, when the query finishes, it’ll recover with a vengeance, loading faster, rendering pages faster, and doing just about everything faster.
The difference could be enough to cure new-computer fever, in some cases.
You can close the Error Console window after it finishes.
What this trick does, from a technical standpoint, is dump all the empty space in the databases where it stores all of your data (bookmarks, browsing history, usernames, stuff like that), making it smaller and easier to manage, and, in turn, faster. Whenever data expires, it’s blanked out rather than truly deleted, so the databases just keep on growing over time, contributing to Firefox’s slowdown.