In the address bar, type about:config and press Enter.
       The about:config "This might void your warranty!" warning page may appear. Click I accept the risk! to continue to the about:config page. 
   Search for plugins.load_appdir_plugins
   Double-click plugins.load_appdir_plugins to change its value to true.

   Click the menu button New Fx Menu and then click Exit Close 29 .
   When you restart Firefox the plugins will be enabled.

Problem: A week or so ago my Facebook AudioChat stopped working, before it always worked perfectly. On Skype it also still works but on facebook i can no longer connect to the other person. Cause: I had Comodo firewall installed on my computer but that came with Geekbudy an ad-maleware aplication. I removed that and after i could no longer connect to the internet. I then reset my winsock and could get on the net again, but firefox would not run. It started but stayed in the background if i looked at my taskmanager. I could get it to start by turning my wireless off by using the knob on top of my Elitebook laptop. When off firefox started sometimes and then i could turn on wireless and work on it but voicechat stopped working Fix: I then searched for a tool to uninstall the left over parts of Comodo firewall and Firefox could run again in a normal way. But audiochat still wont work. So i think some kind of setting within firefox is turned off. Done: I ran hours of anti vir and male and adware scans over my computer and also deleted some. And i turned media on in firefox as i saw that in the question options when creating this question. Tested but that did not make a change. Windows Media or other plugins stopped working after Firefox update The Windows Media plugin is disabled in the latest Firefox. This article explains how to turn it back on. https://support.mozilla.org/en-US/kb/windows-media-or-other-plugins-stopped-working Change a Firefox setting to turn these plugins back on In the address bar, type about:config and press Enter. The about:config "This might void your warranty!" warning page may appear. Click I accept the risk! to continue to the about:config page. Search for plugins.load_appdir_plugins Double-click plugins.load_appdir_plugins to change its value to true. Click the menu button New Fx Menu and then click Exit Close 29 . When you restart Firefox the plugins will be enabled. Here is the topic where i found that i needed to remove more left over parts of comodo. This is a different question but the cause comes from that topic https://support.mozilla.org/en-US/questions/1148777