To get Firefox for Mac 10.4.11 you need to download Firefox 3.6.28 for Mac which is the last version of Firefox to support PowerPC (PPC) Macs. Mozilla has dropped support for Mac OS X 10.4 but Firefox 3.6.28 still works on PPC Macs. Important Note: Running Firefox 3.6.28 on a Mac poses a serious security threat to your Mac. Mozilla no longer issues security updates for it and it has many vulnerabilities that are not suited to surfing online anymore. In addition, Apple no longer supports OS X 10.4 or 10.5 so you run an even greater security risk by using both OS X 10.4 and Firefox 3.6.28.
To run Firefox for OS X 10.4.11, you’ll need the following system requirements:
- Intel x86 or PowerPC G3, G4, or G5 processor
- 128 MB RAM (Recommended: 256 MB RAM or greater)
- 200 MB hard drive space
However, we strongly recommend using TenFourFox to run Firefox on older Macs as it’s far more secure and works a lot better.
TenFourFox: The Best Way To Run Firefox On OS X 10.4.11
TenFourFox is a volunteer project run by diehard Mac fans which effectively allows you to run a more updated version of Firefox (Firefox 17) on OS X 10.4.11. The advantage of TenFourFox is that it’s more like the modern versions of Firefox than Firefox 3.6.28 which means it’s faster and safer. However, the disadvantage is that TenFourFox does not support plugins such as Flash and Java making it unusable with some sites.
TenFourFox works with both Tiger and Leopard, G3, G4 and G5 Macs and supports both HTML5 and JavaScript. Since YouTube now streams videos in HTML5 where available, this means the absence of Flash is not a problem for watching videos on the site using TenFourFox. 
You can download the correct version of TenFourFox for your PowerPC from the TenFourFox download page. Note that there’s a different download depending on whether you are using a G3, G4 and G5 Mac. If you’re looking for Firefox for OS X 10.1.5 to 10.3.9, TenFourFox also offer another Firefox adaptation called Classilla. If you’re also looking for Firefox for Mac OS X 10.5.8, you can find it here.