Things were going great on my Fedora 20 system. My system downloaded a new Shockwave Flash version, which is always good knowing their terrible security problems. But next thing I know my firefox is yelling at me on almost every web page, refusing to start Flash because it’s an old, insecure version. I check my versions and Firefox tells me flash is 126.96.36.1998 (sheesh! Adobe is serious about version numbers) when those last digits are supposed to be .440. I check my flash readme in /usr/lib64/flash-plugin/README and see that it really is 440 installed on my machine. The final piece of evidence comes when I fire up a different profile of my Firefox: this other profile is just fine. It has no flash issues, and reports the correct .440 version.
Knowing it was a profile issue, I navigated to my profile folder at
.mozilla/firefox/[RANDOMDIGITS].[MY_PROFILE], which in this case was named “default” despite the name I’d given it because it was the first profile. Inside the folder I found the
pluginreg.dat file and responsibly displaced it to something Firefox wouldn’t recognize (but I could still recover if necessary) by renaming it
pluginreg.dat.bak, thereby forcing Firefox to rebuild its plugin registry for this profile. Start Firefox on that profile again and problem fixed!