By default your browser history is kept for way too long, which takes up system resources and slows down the browser.  Limiting history size is an excellent way to quickly speed up your browser.

Firefox users:

1. Go to Tools - Options
2. Click on Privacy
3. Then select any number under Keep my history for at least … days. I have it on 7.
4. 
5. Click OK

By the way, if you don’t want to keep any private data at all, simply check Always clear my private data when I close Firefox. To specify what you want cleared, click on the Settings button and check relevant checkboxes.

Internet Explorer 8 users:

1. Go to Tools - Internet Options
2. Under Browsing History click on the Settings button
3. Select a number to keep you browsing history
4. 
5. Before you click OK I would recommend forbidding the browser to check for newer version of stored pages (select Never) and allowing 50MB of disk space to store Temporary Internet Files (the default number is ridiculous).

Enjoy a faster browser!