It is possible to delete the extra installed apps. Disable or remove Add-ons

You can rename (or delete) the mimeTypes.rdf file in the Firefox profile folder to reset all file actions.

• http://kb.mozillazine.org/mimeTypes.rdf
• http://kb.mozillazine.org/File_types_and_download_actions#Resetting_download_actions

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Type about:support in the address bar and press Enter. Under the main banner, press the button; Copy Text To Clipboard.. Then in the reply box at the bottom of this page, do a right click in the box and select Paste. This will show us your system details. No Personal Information Is Collected.

See Applications panel - Set how Firefox handles different types of files. Having many "instances" of Quicktime would be perfectly normal, since the QuickTime plugin can handle many different types of content. I've attached a copy of my own Applications panel.

If you don't want to use the QuickTime plugin for certain types of media, just use the drop-down menu to change the action for that content type in the Applications panel. If you don't want to use the QuickTime plugin for any content, open the Add-ons manager from the Firefox Menu, go to the Plugins panel and set the QuickTime plugin to "Never Activate". Those QuickTime plugin actions will be gone from the Applications panel.

For more information about QuickTime and other plugins, see Use plugins to play audio, video, games and more and Use the QuickTime plugin to play audio and video