I currently have Firefox browser version 12.0 but it says it is the latest version. However I can download version 15.
So why can't I upgrade? or do I have to download version 15 and somehow copy my bookmarks across?
Get latest version of Firefox from here
Follow How to download and install Firefox on Mac for more info!
Not sure if you're still looking for an answer, but it sounds like you need to upgrade Windows....Firefox 12 is the latest version that supports Windows 2000 and Windows XP SP1.
ehart13169, the OP is using Mac OSX 10.8 as per the System Details on right of post.
Sorry, I missed that part...oops.