What is this annoying bar which keeps appearing above Firefox?

[basijan]

I suddenly keep seeing this stupid bar at the top, so I have double controls

How can i remove this thing?

I've checked in system settings - windows and there is nothing obvious really:

I'm using Cinnamon

...


I've disabled the title bar in Firefox customisation menu, and that does work .. until I click and drag the window out of a tiled position, then the title bar reappears!!

I've used cinammon maximus to undecorate using a hotkey - this is a more permanent fix (persists after clicking and dragging), but I have to do it every time I open firefox!

Can anyone please help?

[AZgl1800]

Under 'View', the only thing I have checked is Toolbars > Menu Bar

Everything else is turned OFF.

and as the pix shows, all I have is the Menu and the Tabs and Command line

[basijan]

And on the right hand side? How many minimize, maximize and restore buttons do you have?

This is how it looks in full screen, or if its snapped into place:

After dragging it out of snap:

notice the double title-bar, and window controls

[AZgl1800]

on the Right Side, I have the 'Home' icon, Addons icon, Full Screen, LastPass, uBlock, Facebook Container, FB Purity ( adblock ) and the Hamburger menu of course

[basijan]

I ended up just removing the ff one using css