Well, it’s free, and it works, for MacOS and Windows. It will clean and speed up Firefox, Pale Moon, Chrome, Opera, Thunderbird and Skype as well, with an up to x3 increase in speed. No, it won’t speed up IE or Edge.

Why does it work? It works because with time you get larger and more fragmented databases.

“Firefox (and sometimes it's add-ons) uses SQLITE databases to store lots of its settings. By the time the databases grow and Firefox starts working slowly. SpeedyFox compacts those databases without loosing any data. Databases are optimized to operate faster and are decreased in size.” – CrystalIdea

So…I tried it, and the difference was indeed noticeable. No, I didn’t actually time it. The utility worked quickly…but, depending on the the size of your database, it can take up to an hour. It will inform you how long it took.

Oh yeah…it won’t affect your history, bookmarks, passwords, etc. Also you can run it per browser and per profile. Not bad.

There’s a tutorial here: http://www.crystalidea.com/more-about-speedyfox

You can get it here: http://www.crystalidea.com/downloads/speedyfox.zip