I notice you also have a problem with browsers and PDF files. It sounds like you might not understand the functions of a browser. The very basics is it gets you to where you want to go. Then if a specific program is required to properly display/play or otherwise use what you find, then that program will handle it.
This is determined in Folder options, found in the Control Panel. It is the "Open With" feature that you need to become familiar with. Basically it doesn't matter which browser you're using, applications are set there to open in specific content.
For Firefox: Tools> Content> here is a listing for what Firefox has set to use your Content. For instance:
Find Windows Media Audio or Video File in Content and click to Highlight> look on the right and the choice of which plugin to use is there. All of the Windows Media.........on the left should be set to use the Windows Media plug in in Firefox.
I think once you are aware of the settings in Folder Options and Firefox, you will be able to customize the system as you want it.