Hardware
- Intel Core 2 Q6600 @ 2.4 GHz
- 4 GB, DDR2-800 (3.2 GB addressable)
- 2x 500 GB Western Digital hard disks, RAID-0
- NVIDIA GeForce 8800 GTX, 640 MB
Software
- Microsoft Windows Vista Home Premium SP-1, 32-bit
- Firefox 3 Beta 5 (2008032620)
- Opera 9.50 Beta 2 (9945)
Daily sites
Single results (one tab)
- Firefox 50.888 K
- Opera 169.928 K
Parallel results (multi-tabs opened):
- Firefox 118.896 K
- Opera 213.668 K
Parallel results (multi-tabs viewed):
- Firefox 177.396 K
- Opera 261.020 K
Plug-in heavy sites
Single results (one tab):
- Firefox 90.976 K
- Opera 164.220 K
Parallel results (multi-tabs viewed):
- Firefox 344.488 K
- Opera 391.808 K
Conclusion
The results are surprising. The new king of reduced memory usage is Firefox 3, and not the browser you'd expected it to be, Opera. The Mozilla developers have truly listened to their community and put a hold to the often shouted weakness of Firefox 2, the memory usage (sometimes expressed as leakage by some).
You could argue that you can use the amount of memory that is freely available, but it's no excuse to claim unnecessary memory, as Opera does. Firefox 3's improvements in garbage collection and reducing memory fragmentation have proven that theory works in the real world as well.
http://avencius.nl/content/firefox-3-vs-opera-950-memory-usage