hello, you are probably lacking a right graphics driver for your system. could you go to the firefox menu ≡ > help ? > troubleshooting information, copy the contents of that page and paste them here into a reply on the forum? this might give us a clue what is going on... thank you

Hi Philipp!

Thanks for your response! It turned out it was about the graphics.

Another moderator of this forum advised to turn off hardware acceleration in the browser and it helped!

I think there aren't many people nowadays not having an acceleraton available. :)

Thank you for your help! Beata

you're very welcome - in case some other affected users are reading along, please also see Firefox is slow after updating to Firefox 38 .