Firefox has been working fine then suddenly, I can only download a movie file. Typically, when I clicked on a link, the movie would open in Firefox. Now, when I click on the link, it asks if I want to open it and if I say yes, I downloads the file. I have checked the applications and associated actions and do not see an issue.
The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information.
Note: This will cause you to lose any Extensions, Open websites, and some Preferences.
To Reset Firefox do the following:
Go to Firefox > Help > Troubleshooting Information.
Click the "Reset Firefox" button.
Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
Firefox will open with all factory defaults applied.