On Linux, it is. The Flash plugin on Linux for Chrome is v16. The version for Linux Firefox is 11.2. Adobe stopped supporting Flash on Linux, so Google stepped up to the plate and started bundling Flash with Chrome and supporting it themselves. Flash does still work on Firefox, but at least on my install Click to Run was enabled by default for it (that might be a corporate setting though, I'm not sure".

Regardless, yeah Flash on Firefox on Linux is several years behind.

On linux it's because the NPAPI flash plugin hasn't been updated in a few years. It went Chrome/PPAPI a while back and firefox doesn't support it yet. I think it's supposed to get security fixes but performance issues are never going to get fixed in it.