Provide steps to replicate. The Zoom controls are where?

In the top right drop-down menu (the icon is the 3 horizontal lines)

Much better screenshot. Is that color part of a theme? Did you try Firefox in Troubleshoot Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#search104 Can you log into another account and see if it has the same issue? My mac at work just updated to Sequoia, but I'll check in a few. No issues for me on my Linux computer. see screenshot

Are the keyboard shortcuts "Ctrl +" and "CTRL -" not working as well?

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 "Refresh Firefox" in 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

No issues for me on my work mac. see screenshot