That doesn't sound like expected standard behavior. Start Firefox in Safe Mode to check if one of th

That doesn't sound like expected standard behavior.

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

switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes

do NOT click the "Refresh Firefox" button on the Safe Mode start window

https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode

https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems