As a short-term fix, SandboxSafari should also be able to play
Vimeo videos, but we don't support it and you use it at your own
risk. The ultimate goal is to add H.264 support directly to
TenFourFox, but this is sometime off in the future.
Some video channels, like mine, enable download links on some or all videos. I can't get SD 540p to play in QuickTime Player on my iBook G4 (1.33 GHz, 1.25 GB RAM, Leopard), but 360p works just fine on YouTube (TenFourFox) and Vimeo (downloads).