The next major release of Firefox will not be compatible with Macs running Mac OS X 10.4, also known as Tiger. This comes from a mozilla.dev.planing discussion on Google Groups started by Josh Aas, a Mozilla-employed developer working on the project. The change will go into effect later this year when the browser's Gecko rendering engine makes the jump from 1.9.2 to 1.9.3.

The Mozilla Foundation estimates that there are currently about 1.4 million Tiger users using Firefox 3.5 every day and approximately 36,000 using version 3.6. Those numbers total a little under 24 percent of daily Mac Firefox use.

According to the discussion, Mozilla stopped supporting Tiger on mozilla-central, the most "cutting edge" repository, in September of 2009. Much of the old code was left, however, in case Mozilla had a change in heart. The decision means that the code specific to the old operating system will be removed soon, along with any hope of future 10.4 support.

Users of the open source Web browser who are still using Tiger will be able to continue to use Firefox 3.6 for as long as they want, but the browser will stop receiving updates "several months" after the release of the next major update. This means that any security issues found in the browser after that date would be unlikely to be addressed by the team, and, in turn, left unpatched.

Unsurprisingly, there is a vocal minority speaking out against the move. Individuals with older hardware are no doubt concerned that their old hardware will become even more obsolete and less usable as the rest of the world soldiers on. Mozilla isn't concerned however, citing past data that shows no significant market share loss occurs after support for an older version of the Mac OS has been dropped. The company also claims that it usually supports older versions of Mac OS X longer than most companies.