On mouseover of left arrow of Firefox, some graphic issue..

[ElMugroso]

When I mouse over the left arrow of the Firefox browser, just before clicking, the screen shows some weird geometric lines and pinkish colors 3 or 4, and large triangles (3 or so) of such shade break the screen as if a mosaic.

When I click and Firefox moves to the previous screen, correctly, the phenomenum, is no longer apparent.

I wonder if this is a known issue and if so would like to know what the situation is about, if possible.

It takes about 1/2 second after I place the mouse on the back to previous page arrow for this to happen.

It also happens on the forward page arrow. Most of the time the screen is still readable, but sometimes it is not. Moving the mouse away from the arrows shows the screen correctly.

UPDATE: This actually happens on any clickable area of firefox and the page rendered. For instance, in this forum, if I hover over the "Edit" tag, to edit my post, the phenomenom happens. If I hover over one of the tabs of firefox, ditto, and also over most options.

UPDATE: If I put firefox in full screen mode, then this DOES NOT HAPPEN.

UPDATE: In Opera, this DOES NOT HAPPEN.
Thanks for any help!