This is no big deal for most people out there, except for just a small group of users who still using old PowerPC Mac. I miss the html5 features on my OS X Tiger, espcially location and video playback features.
For some of the Tiger users out there, they may still need the latest web browser, especially for the html5 support. The latest browser that can be installed on OS X 10.4 Tiger is Safari 4.1 and Firefox 3. Both doesn't support html5. Luckily TenFourFox came into rescue.
TenFourFox(10.4Fox) is Firefox 4.0 code base run on OS X 10.4 Tiger, especially for PowerPC Mac. TenFourFox is not just a recompilation for OS X Tiger, it replace some framework coding like CoreText framework which doesn't work well on Tiger. (check the technical differences)
Mac OS X 10.4 Tiger is the last OS X version that you can install on a PowerPC G3 machine. PowerPC G4 and G5 user still can upgrade to Mac OS X 10.5 Leopard.
Is make sense for Mozilla to drop support for older OS X, so they can focus on new framework which came with the later OS X version. It doesn't make sense for some users, if Firefox still works on old Windows XP (2001), it should works on OS X 10.4 (2005).
Again, we saw the power of open-source. With 10.4Fox, I can use location base feature on my OS X 10.4 Tiger on iBook G3.
You can get the latest version here.