Firefox only (Windows/Mac/Linux): Firefox extension RAMBack manually frees up memory from Firefox to keep your favourite web browser running light. Once installed, RAMBack adds a Clear Caches entry to Firefox's Tools menu. When clicked, RAMBack clears the memory cache of sites that aren't in use (like tabs that you've closed). After playing around with it for a bit this morning while keeping my eye on the memory usage in the Windows Task Manager, RAMBack certainly does appear to free up RAM. The smallest drop I saw was around 10MB, while the largest was somewhere over 40MB. RAMBack is free, works wherever Firefox does. If you give it a try, let's hear how RAMBack works for you in the comments.