In this case you’ll need Firefox 3.6 for Mac which was the last one to support PPC Macs but is even older and more vulnerable than Firefox 16. In this article, we look at the risks and problems of using Firefox 16 and highlight what your options are. Some security software will need to be upgraded to a new version for each Firefox version update. Optional software bundled with security software may also need updating. Such software may not be essential for your security, but if outdated, it may interfere with the use of Firefox, or cause Firefox to crash.
Last Updated: January 17, 2015 If you’re using OS X 10.5.8 Leopard then you can still which works on 10.5.8. However, we strongly recommend you upgrade to at least OS X 10.6 Snow Leopard or higher as Firefox 16 is no longer updated by Mozilla and therefore not secure anymore. Note that this only works if you’re using an Intel Mac – if you’re still using OS X 10.5 or 10.4 on a PowerPC Mac, then we recommend. In this case you’ll need Firefox 3.6 for Mac which was the last one to support PPC Macs but is even older and more vulnerable than Firefox 16.
In this article, we look at the risks and problems of using Firefox 16 and highlight what your options are. 
WARNING: Firefox For 10.5.8 Is Not Safe! Since Firefox 17 until the latest version of Firefox, you need at least OS X 10.6 Snow Leopard or higher to run the browser safely and efficiently on your Mac. We emphasize that using Firefox 16 is not a good idea because it is no longer updated or supported by Mozilla leaving it vulnerable to attack, malware, spyware and other online threats. Not only this, but you’ll also find that many add-ons or plugins simply won’t work with it anymore.
If you want to see just how many security threats have to be fixed on a regular basis by Mozilla, check out the. Mozilla take security very seriously and it’s also worth checking out the to see some of the work that goes into keeping Firefox safe.