There has been a change in where Firefox searches for plugins and the plugins folder in the Firefox program folder is no longer scanned for plugins, so Firefox won't find them anymore if they are installed in the plugins folder instead of the "browser\plugins" folder that Firefox now scans.

You can set the plugins.load_appdir_plugins pref to true on the about:config page to make Firefox scan the "<install>/plugins/" directory for plugins like the WMP plugin (np-mswmp.dll).

You can alternatively move plugins from "<install directory>\plugins\" to "<install directory>\browser\plugins\" to make Firefox find them again.

• http://www.ghacks.net/2013/05/15/why-you-may-have-lost-access-to-plugins-or-extensions-in-firefox-21/
• http://mike.kaply.com/2013/04/24/major-changes-coming-in-firefox-21/

The folders you mentioned. don't exist for Macs. Hopefully The version for Macs isn't looking there.

Can you check out the pluginreg.dat file in a profile that is still working to see where this plugin is installed?

• http://kb.mozillazine.org/Profile_folder_-_Firefox

Browser plug=ins for the Mac are stored in /lLibrary/Internet Plug-Ins where they've been for years. What is strange about this problem is, FF recognizes other plug-ins in the same folder including the Quicktime plug-in for user accounts that existed before FF 21.0 is installed and it still recognizes the plug-ins in that folder except for the Quicktime plug-in for user accounts created after FF 21.0 is installed. It happens on two different Macs I have with two different OS's. It also happened for someone at Apple tech-suppot while I was on the phone with him.

oops Library*

So, this plugin doesn't appear as blocked in Tools > Add-ons > Plugins?

Try to delete the pluginreg.dat file in the Firefox Profile Folder and maybe addons.sqlite as well to reset the plugin registry databases.

See "Re-initializing the plugins database":

• https://support.mozilla.org/kb/troubleshoot-issues-with-plugins-fix-problems

Does it work if you copy the pluginreg.dat file from a working profile to a not-working profile?

Well I tried everything you mentioned before I even posted this other than trying to copy a working pluginreg.dat file to a non-working profile. That's a bit tricky seeing I would have to do it as root which isn't snabled on my Mac and a pain. Or conversely I could email myself the file, login to the non-working user and see what happens. I've already spent hours on this issue and from what the Apple tech support person and myself saw by doing a Google search this is becoming a commonly reported problem.

If I feel like playing with it more I will post the results.

as it turns out using a working pluginreg.dat file in place of a non-working one does fix the problem. now all someone at Mozilla has to do is figure out why.

I've also noticed on Linux that Firefox sometimes seems to have problems with picking up plugins correctly in some cases. Sometimes it works, but in other cases it doesn't work. I'm not sure if this is profile related or Firefox version related.

I couldn't say but I'm guessing it is the FF version. I didn't have this issue before 21.0. And I find it odd it only seems to be the Quicktime plugin in the Mac's case. So far anyway. Btw, Aurora has the same problem and I didn't check but I bet the nightly builds do as well.

I'm just thinking that this is a significant bug because, if you have a brand new Mac and install FF 21.0 as the first FF on your Mac, it won't see the Quicktime plugin. I actually know this to be true because in the process of tracking this problem down, I was talking to an Apple tech support person who installed FF for the first time and it didn't recognize the Quicktime plugin.

Although replacing a working pluginreg.dat file for the non-working one fixes the problem, it doesn't help if it's a fresh install seeing you wouldn't have a working pluginreg.dat file.