Does your browser eat too much memory?

Suspend your inactive background tabs and disable extensions/add-ons that you don't use. You won't miss them and if you need them, you can unsuspend/enable them.

Chrome Users: The Great Suspender
Firefox Users: Suspend Tab

Don't need your browser open for a while, but still want to keep track of where you were before you went afk? You can save your browsing session, close your browserand continue later.

Chrome Users: Session Buddy
Firefox Users: Session Manager

Is your browser's memory usage still excessive? Try relegating your browser processes to one tab with this extension/add-on.

Chrome Users: OneTab
FireFox Users: OneTab

If you're still having issues, you may be having problems with your browser or the website you are visiting;though the problem is usually that the device you are browsing on is not powerful enough.
This isn't a support thread, so if you have any questions please ask the respective add-on/extension developer(s), or contact Google or Mozilla directly.