hello juandfuca, does it happen too when you launch firefox in safe mode once? [[Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems]] maybe it's an issue with hardware acceleration. you could either try [[Upgrade your graphics drivers to use hardware acceleration and WebGL|updating your graphics driver]] (you'll probably get the most up-to-date one from your graphics card manufacturer's website) or disabling hardware acceleration in firefox > options > advanced > general.