I am running 10.5.8 on OSX and Firefox 5.0.1. and cannot upgrade to the latest Yahoo Mail.
When trying to upgrade, I see the following error message: You're almost there, but your web browser doesn’t support the newest version of Yahoo!7 Mail
Upgrade to a faster, more secure version of a supported browser. It's free and it only takes a few moments:
Firefox Internet Explorer (for Windows) Safari
Clicking on 'Firefox' in the error message, leads to another error message which says: Mozilla Firefox Optimised for Yahoo!7
Sorry, Mozilla Firefox optimised for Yahoo!7 is not available for your system.
The Yahoo!7 optimised version of Mozilla Firefox is only available for the following operating systems:
Windows 2000 Windows XP Windows Server 2003 Windows Vista Windows 7 Mac OS X 10.4 or later Linux
See the System Requirements for more details on hardware and software requirements and recommendations.