Does this only happen when you use the Ctrl+T keyboard shortcut or also if you open a new tab via other ways like the plus button if you make the Tab bar appear? I can't replicate this with the official Mozilla version, so it is possible that the version you use from the Ubuntu repositories behaves this way. Start Firefox in <u>[[Safe Mode|Safe Mode]]</u> to check if one of the extensions ("3-bar" menu button or Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem. *Switch to the DEFAULT theme: "3-bar" menu button or Tools > Add-ons > Appearance *Do NOT click the "Refresh Firefox" button on the Safe Mode start window *https://support.mozilla.org/kb/Safe+Mode *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes Try the Firefox version from the official Mozilla server if you currently use a version from the repositories of your Linux distribution. *https://www.mozilla.org/en-US/firefox/all/