Mozilla stopped supporting Mac OS X 10.4, aka Tiger, in September 2009, but left a large amount of Tiger bits in the development code. Now, said Josh Aas, a platform engineer for Mozilla who works on Mac OS X integration, it's time to either restore support for the five-year-old operating system or remove the code from the development tree.

"We would like to take advantage of more modern technologies on Mac OS X and 10.4 support has been a hindrance," said Aas in a message yesterday on the forum. "Where we can work around supporting 10.4, doing so consumes valuable time and effort. Neither Chrome nor Safari has to deal with this."

According to Mozilla's metrics, 24% of those running the Mac version of Firefox 3.5 rely on Tiger, while 12% of those running the just-released Firefox 3.6 do. Half of all users run Firefox 3.5 on Mac OS X 10.5, aka Leopard, while 59% run Firefox 3.6 on OS X 10.6, or .

Aas noted that Tiger users can continue to run Firefox 3.6, which supports the older operating system, until that version is retired from support. Currently, that end-of-support would come sometime in 2011, as Mozilla doesn't expect to to its open-source browser until late this year at the earliest. Mozilla's policy is to support an edition for approximately six months after a new version ships.

"We are often one of the last vendors to continue supporting older Mac OS X releases," said Aas.