On Firefox on my recently upgraded to Windows 10 PC? Works fine on phone, tablet and and windows 7 PC. I have just installed a completely fresh copy on another Windows 10 PC and I get the same mess. See screenshot.
Just installed FireFox on my Windows 10 laptop and no issues (even going to exactly the same page that you screenshotted). So I'd reset all of FireFox's settings, make sure it's up-to-date and do a restart.
Turned out it was Kaspesky throwing a spanner in the works. Posted on the Mozilla forum and recived a walkthrough on how to resolve this issue.