Just in case you do not know, or you are interested, the Firefox's UI is mere CSS, one can customize it through "chrome/userChrome.css" in the profile folder of

Just in case you do not know, or you are interested, the Firefox's UI is mere CSS, one can customize it through "chrome/userChrome.css" in the profile folder of the user. I put for example my tabs under the bookmarks, just above the page content (As FF used to be at past), with the template from the CustomCSSforFx[1] project, and modified some colors and icons. Firefox have also the "Browser Toolbox"[2], homologous to the web development tools, that one can use for to explore the css of the UI, select elements, etc, and modify them for to see how would look the modifications before to put them within the userChrome.css The tabs I think that are under the id=TabsToolbar, so an #TabsToolbar{ display: none !important; } or similar should work, in addition to correct with other css params the space that it leaves. Note: What happens is they change things from time to time, and after an update one have to correct the css again, I warn. [1] https://github.com/Aris-t2/CustomCSSforFx https://github.com/Aris-t2/CustomCSSforFx [2] https://firefox-source-docs.mozilla.org/devtools-user/browser_toolbox/index.html https://firefox-source-docs.mozilla.org/devtools-user/browse...