Click on the "Tools" menu in Firefox and select "Add-ons" to temporarily disable the QuickTime plugin without fully uninstalling it. Select "QuickTime Plugin." Click the button to the right of the selection labeled "Disable." The plugin can be enabled with another click.
Type "about:config" in the browser's location bar and hit "Enter" to manually remove the Quicktime plugin from within Firefox. Depending on your system's configuration, a button may pop up that reads "I'll be careful, I promise!" Click the button to confirm.
search for or scroll down to "plugin.expose_full_path." Double-click on the value "false" to the right of "plugin.expose_full_path" to change it to "true."
Type "about:plugins" in the browser's location bar and hit "Enter." Scroll down the list to QuickTime. There will likely be several QuitckTime plugins listed.
Note the file listed next to each QuickTime plugin on the list. For example, the listing may be "C:\Program Files\Mozilla Firefox\plugins\npqtplugin2.dll."
Navigate in Windows Explorer or Apple Finder to each of the QuickTime plugin files you noted in Step 5. Delete or change each file name. For example, you can change "npqtplugin2.dll" to "XXnpqtplugin2.dll."
Close the Explorer or Finder windows and restart Firefox. The QuickTime plugin should now be uninstalled.