Firefox isn't able to show images correctly

Hello there, I noticed that some images are not shown correctly in Firefox, in practice they are shown as striped boxes... In addition online games seem affected by the same problem... I upload two screenshot taken when I was playing at slither.io. The image taken on firefox show that each worm is a "rectangle" and the map in the bottom-right corner is unreadable, instead on Microsoft Edge the worms are smooth and the map is definetly better... I think the problem is related to some settings, since it happens both on windows and on linux... Please tell me if I have to post others screenshots... Thanks