You are welcome. Yosemite will give you Safari 8.0.4, which should allow you access to Yahoo mail. Yosemite is different than Snow Leopard, so you might want to try it before replacing 10.6. Yosemite doesn't act like Snow Leopard. For example, scrolling is reversed, but can be changed. If you spend enough time in System Preferences, you can get the OS to be mostly like Snow Leopard.
One option is to create a new partition (~30- 50 GB), install the new OS, and ‘test drive’ it. If you like/don’t like it it, you can then remove the partition. Do a backup before you do anything. By doing this, if you don’t like it you won’t have to go though the revert process.
Check to make sure your applications are compatible.
Application Compatibility
Applications Compatibility (2)