Try to rename/remove handlers.json and delete mimeTypes.rdf if present in the Firefox profile folder with Firefox closed to reset all file actions.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

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

cor-el said

Try to rename/remove handlers.json and delete mimeTypes.rdf if present in the Firefox profile folder with Firefox closed to reset all file actions. You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

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

Unfortunately, this did not seem to solve the problem. I still can't set .gif files on my computer to open with firefox unless I open them from firefox. I just finished trying this action, I will update if this changes.

I don’t think any Firefox version registers the .gif file type for itself during install, where (perhaps) it used to do so years ago if I remember well. Also, the list you referred to describes settings for MIME types, not file extensions (see this page for more).

If you want to set Firefox as your default program to open gif files, you need Windows to instruct it as such, and make sure other programs do not (i.e. unregister them) if needed. The way you tried this should work in Windows, and you should also be offered a "Always use the selected program..." prompt from that. Do make sure to point to the firefox.exe program, not one already offered in the list by Windows. It probably does not recognize Firefox as an image viewer, hence it may not appear there.

You may however wonder whether or not it’s good to set Firefox as a default program for this purpose - some people prefer to keep the original program and just drag e.g. a .gif or .png file to Firefox when needed / occasionally.

Tonnes said

I don’t think any Firefox version registers the .gif file type for itself during install, where (perhaps) it used to do so years ago if I remember well. Also, the list you referred to describes settings for MIME types, not file extensions (see this page for more). If you want to set Firefox as your default program to open gif files, you need Windows to instruct it as such, and make sure other programs do not (i.e. unregister them) if needed. The way you tried this should work in Windows, and you should also be offered a "Always use the selected program..." prompt from that. Do make sure to point to the firefox.exe program, not one already offered in the list by Windows. It probably does not recognize Firefox as an image viewer, hence it may not appear there. You may however wonder whether or not it’s good to set Firefox as a default program for this purpose - some people prefer to keep the original program and just drag e.g. a .gif or .png file to Firefox when needed / occasionally.

I did point to firefox.exe. When I select the .exe the window closes and I'm left with the (open with..). Window as if I had not selected browse or navigated to a program. There is no prompt or error message. What I would normally expect is that the windows would close or give me the option to always use this program or something like that and when I open .gif files they open with Firefox web browser. This is not happening and I have no clue why.

Interesting. Did you recently switch Firefox from the 32-bit to 64-bit version perhaps?

If so, uninstall Firefox from Add/Remove Programs (you won’t lose personal settings), make sure there is no 32-bit version installed too (uninstall if so), and reinstall the 64-bit version from here.

I found this suggestion here - the thread may be useful for other suggestions and info.

Tonnes said

Interesting. Did you recently switch Firefox from the 32-bit to 64-bit version perhaps? If so, uninstall Firefox from Add/Remove Programs (you won’t lose personal settings), make sure there is no 32-bit version installed too (uninstall if so), and reinstall the 64-bit version from here. I found this suggestion here - the thread may be useful for other suggestions and info.

I did not recently upgrade that I know of, I don't know if Mozilla maintenance service may have done. I had tried uninstalling and re-installing, but I have tried it again. I uninstalled Chrome, disconnected form my wifi network, Ran TFC cleaner by old timer, and uninstalled Firefox and Mozilla maintenance service from control panel. I also deleted the Maintenance service folders. I downloaded and reinstalled with the link you provided using internet explorer and I still get the same results. If anyone has recreated this problem, let me know.

What happens when you drag a gif into the screen from a folder or desktop ? An animated one. It should play or see. I can always see it. This is how your going to have to use it if it works for you like that.

Dragging should probably work nevertheless as well as choosing File > Open File… - I think this is a known Windows issue.

- Apart from uninstalling the Mozilla Maintenance service (that should not be necessary as that should go happen with uninstalling/installing Firefox), did you actually uninstall Firefox itself properly too, i.e. using Add or Remove Programs in the Control panel?

- Are you sure there are no Firefox installs listed there, and (perhaps more important) no remaining Mozilla Firefox folders in both C:\Program Files and C:\Program Files (x86) when using a file explorer?

- Recently Mozilla has moved 32-bit Firefox users to 64-bit in 56.0.1, so this could have happened automatically. The point is, also looking at this question/thread at Microsoft (expand all replies and also click "this post" written on Dec 20 2012), the exact issue can occur if the actual program cannot be found, so that could be fixed by (quote) "moving the program from the folder "Program Files (x86)" to "Program Files"" (better: make sure to install to the proper folder only rather than moving files), or by fixing the registry entry manually.

In other words, if for some reason Windows still looks at C:\Program Files (x86)\Mozilla Firefox for the former 32-bit install) instead of C:\Program Files\Mozilla Firefox that should now contain the 64-bit version, it will not allow you to register it for handling .gif files. You can imagine if there is a firefox.exe in an older 32-bit folder that may not have been removed - but is still known to Windows and selected each time by you - the issue could persist.

Tonnes said

Dragging should probably work nevertheless as well as choosing File > Open File… - I think this is a known Windows issue. - Apart from uninstalling the Mozilla Maintenance service (that should not be necessary as that should go happen with uninstalling/installing Firefox), did you actually uninstall Firefox itself properly too, i.e. using Add or Remove Programs in the Control panel? - Are you sure there are no Firefox installs listed there, and (perhaps more important) no remaining Mozilla Firefox folders in both C:\Program Files and C:\Program Files (x86) when using a file explorer? - Recently Mozilla has moved 32-bit Firefox users to 64-bit in 56.0.1, so this could have happened automatically. The point is, also looking at this question/thread at Microsoft (expand all replies and also click "this post" written on Dec 20 2012), the exact issue can occur if the actual program cannot be found, so that could be fixed by (quote) "moving the program from the folder "Program Files (x86)" to "Program Files"" (better: make sure to install to the proper folder only rather than moving files), or by fixing the registry entry manually. In other words, if for some reason Windows still looks at C:\Program Files (x86)\Mozilla Firefox for the former 32-bit install) instead of C:\Program Files\Mozilla Firefox that should now contain the 64-bit version, it will not allow you to register it for handling .gif files. You can imagine if there is a firefox.exe in an older 32-bit folder that may not have been removed - but is still known to Windows and selected each time by you - the issue could persist.

I feel a little silly because I think you are right. I installed 32 bit and it works fine. I suspect I can now install 64 bit and make sure it is being installed in the proper place. I did not have any folders left from uninstalls besides the mozilla maintenance service. I seem to remember that mozilla maintenance service was a separate uninstallable program. I can't remember, but I removed it.

Thanks