Its not a theme or add on. This is 123.0 64 bit running

This is possibly a problem with your userChrome.css file in case you use this file to style Firefox. You can check if there is an update available from its creator.

More info about userChrome.css/userContent.css in case you are not familiar:

• https://www.userchrome.org/what-is-userchrome-css.html

This is possibly a problem with your userChrome.css file in case you use this file to style Firefox. You can check if there is an update available from its creator. More info about userChrome.css/userContent.css in case you are not familiar:

• https://www.userchrome.org/what-is-userchrome-css.html

The thing is, is that I haven't tried to style Firefox with anything

This still looks weird to me. Is that the only part that looks this way since you only showed a small part of your screen?

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the Default System theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems