This is a very common problem and is mainly due to fragmentation of databases. SpeedyFox is a freeware utility that fixes this problem with a single click. It will speed-up Firefox’s startup time, speed-up browsing history and the operations with cookies will be faster.
After installation, it will automatically detect your Firefox’s default profile. If you have more than one profile, you can select the one you want to optimize from the drop-down menu.
All you have to do is select the default profile that you want to optimize and hit Speed Up Firefox button.