On the security front, there are five security advisories rated as critical for Firefox 11. The critical flaws fixed include a use-after-free memory flaw in shlwapi.dll and what Mozilla refers to as, 'miscellaneous memory safety hazards'.
Memory errors were also found in Firefox's handling of SVG graphics. The SVG flaws were discovered by using Google's open source Address Sanitizer tool. The AddressSanitizer is a memory error detector for C/C++ and is able to help identify out-of-bounds access issues as well as use-after-free memory conditions.
It is fast and works well!
Also, Seamonkey 2.8 is just out. I don't know that it is directly based on FF 11 but it is closely following Firefox development. I don't expect big or, even, noticeable changes, just hope it keeps working! 