Go to about:plugins and find a proper path to add a file. Create a new subfolder 2.1.1 with that dll, then change the version in about:config.

Thank you so much. It worked.

For people That want step by step here is how I did it (With the help of TYDraniu) Step 1. Go to "about:plugins" without the quotes Step 2. Find the plugin OpenH264 and copy the path. Step 3. Open file explorer and go the folder location. (Don't go in the folder of the version its most likely 1.8.1.1 but just go the dir above.) Step 4. Add a new folder with the Version number of the dll. Example, 2.1.1 was the latest version the the dll I had. Step 5. After you made the folder put the .DLL file in the new folder. Step 6. Open Firefox and type in the address bar "about:config" without the quotes and say yes to the risk and search "media.gmp-gmpopenh264.version" without the quotes and put in the version of the dll's folder. DONE! Go into plugins in settings and add-ons and check the version number says. If it is the version you just installed YOU did it! if not, reply back and I will be happy to help.

DVT

I have a new problem with this. Firefox keeps bring back the old version (1.8.1.1) even if I say no automatic updates.