Before downloading Firefox 7 - Here's Full Changelog :
Firefox 7 uses less memory than Firefox 6 (and 5 and 4): often 20% to 30% less, and sometimes as much as 50% less. In particular, Firefox 7′s memory usage will stay steady if you leave it running overnight, and it will free up more memory when you close many tabs.
This means that Firefox 7 is faster (sometimes drastically so) and less likely to crash, particularly if you have many websites open at once and/or keep Firefox running for a long time between restarts.
Download Firefox 7 for Windows, Mac and Linux - Links :Download Firefox 7 for Windows
Download Firefox 7 for Linux
Download Firefox 7 for Mac