I'm using Windows 7 and I have multiple browsers installed (Firefox, Firefox Light, Internet Explorer and Chrome).
Since 2 days ago, CSS are not displayed properly on all websites in all browsers except Chrome (no background, no colors, no backround images, only black and white fonts, ...).
I've tried to reinstall Firefox with no success (with new profile).
I've tried to disable extensions like AdBlock and I've tried to disable all Antivirus/Firewall software who could be the cause of this, but with no success.
I haven't found any suspect process as well in my task manager.
So what should I look at to solve this problem ?
Could it be introduced by the Windows 10 updater to push me to migrate from Windows 7 to Windows 10 ?
EDIT : the problem is affecting other applications like MS Excel : I can't set background color for a cell anymore for example.