Hi Chris_N, that panel definitely should not open, close, or reload by itself. There are many keyboard shortcuts that will open it, and two that will close it, so possibly Firefox thinks those keys are being pressed, or they are being sent to Firefox by another application or device.

General toggles (once to open, once to close):

• Ctrl+Shift+i
• F12

Specific tools:

• There are many shortcuts to open specific sections of the tools. If you open the menu and expand Web Developer, they should be listed there.

Does that help point toward the source of the issue?

JScher, Thanks for your suggestion. Either of the two keystrokes turns it off... for a time... But if I am idle for an hour or so, it starts up again. Each time, your keystrokes stop it, but can you suggest a more permanent fix? I block all the pop ups, tracking, etc that I can, and I've noticed recently (after a Win10 update) that in the boot up process a long list of .dlls get 'access denied.' I don't see any connection, but maybe there is one?