hello bramversluis129, please go through the troubleshooting steps at Websites look wrong or appear differently than they should (especially the part about checking that javascript is enabled and making sure that you have no extensions installed in firefox > addons > extensions that might block it).

I already did, nothing worked! Look at my photo:

is the same thing happening, when you launch firefox in safe mode once?

Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

Madperson, thanks for your help. Om some reason the problem solved.... And i changed nothing...