A while back I experimented with Yahoo Mail Beta after learning of a trick from CyberNet to trick Yahoo into offering their Mail Beta. While I did like the interface which is similar to that of Outlook and Thunderbird it did tend to run a bit slow when it first loaded and causes my Firefox 2.0b2 to use a lot of memory. A couple items of interest the ‘bulk’ folder has been renamed to ‘spam’ and you can also view RSS feeds within the Mail application.
Yahoo has now made their mail Beta available to all. The performance has improved somewhat, but still can be slow loading. Sadly though it still causes Firefox to use a lot of memory (granted not as bad as the leaks in 1.5.0.X did). Now, keep in mind this is still beta and it ain’t going to be perfect, but it does have a lot of potential. Yahoo made great strides on their Beta version of Maps so hopefully with a few more improvements their Mail will be just as good.
For more information checkout CyberNet Tech News article: Yahoo Mail Beta Opened To The World
The Firefox Extension Guru's Blog 
Are people really still using Yahoo mail?
Yes, I still am and don’t plan on stopping. Never cared for GMail and the MyWay e-mail does not work correctly.
[…] This extension works with Firefox builds 0.9.0 up to the current 1.5.0.X builds. There were some issues when users went to Firefox 1.5.0.7, but there are directions on the developers home page on how to get around this. Also, this extensions can be forced (I have done so successfully) with Bon Echo (Firefox 2) with the Nightly Testers Tools extension. Also a nice alternative to the Yahoo Mail Beta. Posted by ffextensionguru Filed in Yahoo, Mozilla Firefox, Extensions […]
[…] some issues with MyWay e-mail, they were nothing compared to those I experienced when I switch to Yahoo Mail Beta when it was released to all. The Beta version is Flash based and is to offer a similar layout as […]