- Type about:config in the address bar.
- Just accept the scary warning.
- In the search bar at the top of this page, look for browser.sessionrestore.max_concurrent_tabs.
- Click OK, close Firefox and open it up again.
- The setting is saved, and you will find a bit of an improvement.
If you want to speed up your web browsing speed without doing much, look at these articles:
Beginners' Guide to choosing a DNS server for faster web browsing
Use QoS on your network to give your programs the bandwidth they need