Please uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Then restart system. Then run Windows Disk Cleanup. (Note: This should be Pinned and run Weekly, If never done below expect 10's of gig's) Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. But you should make a back up before you do :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Reinstall with Current Release Firefox 57.0.4 with a Full Version Installer

• https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.

Can't uninstall Firefox! I click uninstall, a screen pops up to ask: 'Do you want the app (Firefox Helper), to make changes to your device? Whether I click yes or no, I'm just sent back to the modify/uninstall option, and so around I go again!

Hi, try a Clean Reinstall; this means you remove your Firefox program files and then reinstall Firefox. This process does not remove your Firefox profile data (such as bookmarks and passwords), since that information is stored in a different location. With Firefox closed, use another browser to download Firefox from https://www.mozilla.org/en-US/firefox/all/ and save the file to somewhere convenient on your computer.

Now delete the Firefox installation folder which should be in one of the following locations -

C:\Program Files\Mozilla Firefox C:\Program Files (x86)\Mozilla Firefox

You can now double click the file you previously downloaded to install Firefox.

If your question is resolved by this or another answer, please take a minute to let us know. Thank you!

I cannot delete c:\program files (folder or a file is open in another program), or c:\program files (86) (you need permission from trusted installer). Still unable to uninstall Firefox.

Just try downloading FF from https://www.mozilla.org/en-US/firefox/all/

Bit of a long shot: Make sure Firefox isn't running in the Task Manager (Ctrl+Shift+Esc). If it is, stop it, then try to delete the folder again.

Trusted Installer is part of Windows Modules Installer, and I don't know why you are getting that error unless some Windows files have got corrupted, so try running System File Checker https://support.microsoft.com/en-gb/help/929833/use-the-system-file-checker-tool-to-repair-missing-or-corrupted-system

I'm still unable to uninstall Firefox, I need 'elevated permissions' to run DISM.

Should I just install the latest version of Firefox, or maybe switch to Chrome?

Boot into Safe Mode with Networking and uninstall FF. Sounds like your install is corrupted.

Note that Firefox 58 will be released next Tuesday.

Let’s do a full clean re-install;

Download Firefox For All languages And Systems {web link}

Save the file. Then Close Firefox.

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86)

Mac: Open the "Applications" folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux

If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one.

Do Not remove the profiles folder.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ If there is a problem, start your Computer in safe mode and try again.

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia

Try to run the Firefox program once as Administrator (right-click: Run as Administrator) in case some updates are pending.