Greys bars displayed with scrolling

Hi everyone,

I'm from France and I come here because I have a very strange issue since a few days.

With Firefox, when I scroll, I see these strange grey bars :



When I go lower to quit the screen zone when to problem appears and I come back to it, everything is back to normal.. Sometime, it's even parts of the page (pieces of pictures and texts) which are retain on the screen.. I sroll down and I scroll up again, and nothing is left, everything is normal.

I observe this phenomenon only with Firefox and Twitter. Everything seems to be okay with other browsers (Chrome, Opera, Safari..).

I try to deactivate all the addons, to re-initialise Firefox.. same problem.

I don't think it's an hardware issue, isn't it ?

Configuration :

OS X 10.10.4

iMac 27" late 2013 (bought december 2014)
CPU : 3.5 GHz Intel Core i7
RAM : 32 Go 1600 MHz DDR3
GPU : Nvidia GeForce GTX 780M 4096 Mo

Firefox 39.0

All the updates are done via App Store.

Any ideas of the nature of the problem ?

Thanks for your help.

Regards.

 

Hello everyone,

I have an iMac 27" late 2013 (bought in December 2014). Since a few days, I noticed graphic bugs.

Like this but only with Firefox on Twitter :



And I got something like this twice since yesterday :



Is a software issue ? I hope that it's not hardware. I never got issues like this before. Maybe it's related to my 10.10.3 to 10.10.4 update ?

I ran Apple Diagnostics (D key on boot) and everything seems to be okay.

Thanks for your help.

Regards.

microdog