Firefox 68 introduces a new launcher process that reduces the browser to running as a standard user (medium integrity). A program running with standard user privileges can't write in certain places on the system. (Having UAC disabled also causes problems with drag-and-drop, but that's a different issue.)

More info: Drag and Drop errors with Firefox Launcher Process enabled and Windows UAC disabled - How to Fix

If your work routinely requires you to save to the root of the C drive, you can override the privilege reduction by starting Firefox with a command-line switch. This bypasses the new security feature and forces Firefox to run the browser with full user privileges. The simplest method would be to modify your Firefox program shortcut (assuming you start Firefox from the program shortcut, and not from a link). Either:

• Right-click a Firefox desktop shortcut, then click Properties
• Right-click a Firefox icon pinned to the Taskbar then right-click Mozilla Firefox, then click Properties

Windows should show the Shortcut tab and select the Target field. The Target usually is along the following lines:

• "C:\Program Files\Mozilla Firefox\firefox.exe"
• "C:\Program Files (x86)\Mozilla Firefox\firefox.exe"

You would add a space and then the new switch, either:

• "C:\Program Files\Mozilla Firefox\firefox.exe" -no-deelevate
• "C:\Program Files (x86)\Mozilla Firefox\firefox.exe" -no-deelevate

Success?

Thank You. Perfect explanation Worked PERFECTLY.

I was fine with all prior versions of Firefox. But this happened to me with the new 71.0 (64) update (unable to drop and drag anything - images, links, etc - to desktop or any file folder). The "-no-deelevate" alleviated the problem.

Guess instead of fixing the issue, Firefox has expanded the number of systems which will suffer from the problem.

Hi blspro, you didn't mention your OS. Are you also on Windows 7, or are you on a newer version? Have you modified the Windows UAC settings or are you using the Windows default UAC settings?

Hi jscher

This is the latest version of Windows 10 Pro (64). The UAC is set to "enabled" - as it has been since the installation of Win10 multiple years ago now (not to mention through all its subsequent updates). And, as I noted, everything has been working fine all those years. It was only after the newest Firefox update that the "drop and drag" problem arose.

Hi blspro, I guess for some reason your File Explorer is running with elevated privileges.

I guess for some reason your File Explorer is running with elevated privileges

Some unknown "privileges" which were never a problem for Firefox until Mozilla made some unknown change to Firefox for some unknown reason.

shrug:

At least the problem could be circumvented. But it seems FF is breaking its functionality for more and more people.