http://ftp.mozilla.org/pub/firefox/releases/

But I hope you aren't connecting this system to the Internet. OS X 10.8 has been effectively unsupported for years and is rife with serious vulnerabilities that will never be fixed. Same with old versions of Firefox... you are very literally begging for trouble. I cannot urge you strongly enough to update your OS.

For the time being, you can use the Extended Support Release of Firefox 45, which will still receive security updates for several months. More info: Firefox support has ended for Mac OS X 10.6, 10.7 and 10.8.

Thank you both for your replies. I have a very good antivirus program and have not been hacked even using this older OS X 10.8.5. I check it every other day, every day some times even. I have read of various problems with OS X 10.9 and above. Also, this old iMac is a late 2009 model. It only has 4G ram. I have had it in a good shop this year to have it checked as I did have a minor problem. The technician did a complete check up and said it is running great and had no nasty viruses or any other malware. I also use a separate Malware program at least twice every week. I do not have much confidence in the newer Mac OS versions. Also, I have used Windows based computers in the past and will never go back to any Windows computer. OK, FYI I am 69 year old and have no reason to buy a newer iMac and from what I have read of the newest version of Mac OS, it stinks. Same applies to the two previous versions of Mac OS X. Possibly OS X 10.9 may be a future upgrade, but not yet. When this OS works well for me, old age remember, why change? I apologize if this comment sounds negative, I don't mean to be like that. Just trying to tell you why I use this version of OS X and keep using this older iMac. I detest tossing out anything that still works just because there is a newer version with more "bells and whistles" that I will never use or even have any need of. Yeah, you can call me a grumpy old guy. Again, thank you both for your replies. charlie aka; bear47