Firefox has a reputation for being a memory hog, but the beta version of the upcoming Firefox 7 browser, currently available for download, has been designed to perform faster by using less memory resources. The efficiency with which Firefox uses memory has varied over the years. For example, Firefox 2 was quite bad, but Firefox 3, 3.5 and 3.6 were substantially better. But Firefox 4 regressed again, partly due to a large number of new features (not all of which were maximally efficient in their first iteration), and partly due to some over-aggressive tuning of heuristics relating to JavaScript garbage collection and image decoding. According to Mozilla, 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, Mozilla claims.

This means that Firefox 7 is faster 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.

Besides the drastically improved memory use, the latest version of Firefox Beta has the following changes:

- Drastically improved memory use
- Added a new rendering backend to speed up Canvas operations on Windows systems
- Bookmark and password changes now sync almost instantly when using Firefox Sync
- Added support for text-overflow: ellipsis
- Added support for the Web Timing specification
- Added an opt-in system for users to send performance data back to Mozilla to improve future versions of Firefox. This can be enabled by installing an add-on
- Fixed several stability issues