I swear, if developers keep adding decimals to their versioning systems, I might just have to start a petition or something. Firefox 220.127.116.11.18.104.22.168 is available with "improvements to product stability" and several security enhancements. I believe it should be available via Firefox 1.5's built-in updating system, or simply from Mozilla's Firefox page.
[note: extra '.22.214.171.124' added for humor. Not intended as a real software versioning system - yet]