Mouse Cursor while Holding Middle-Mouse-Button has translucent rectangle around it

[Accname]

What the title says.
When I hold down middle mouse button to scroll through the page there is a translucent rectangle (with a shadow even!) around the mouse cursor that appears.

I tried to make a screenshot of the cursor but no matter what I try the screenshot will not show the cursor. DAMN YOU!

I hope this is reproduceable by others.

Edit: Can be closed. Turns out, this seems to be a problem with my firefox. For some reason it apparently broke today...

 

[tom_mai78101]

As you wish, my lord.