What are some other things you do not like about Firefox 12 besides the apparent incompatibility with the latest Adobe Flash Player pllugins? Or is that the main reason you don't like it?
I forgot to mention that, after I reverted Firefox back to Version 10, and installed the matching flash plugins, I found another problem that I corrected, in order to make the Yahoo videos play. Under Firefox Tools and Options, I unchecked "Enable Javascript". I don't know what that did, but it worked.
It seems that Adobe and Mozilla need to get together about compatibility issues between the latest flash plugins and Firefox 12. It may have something to do with Windows 7, also. I have Win7 64 bit. Adobe's latest plugin combines 32 bit and 64 bit, but I don't believe the 64 bit part of it is compatible with Windows 7. Therefore, the older flash plugin combined with an older version of Firefox worked. But, maybe someone has a better explanation for it.