Firefox's style or appearance can be modified by creating a chrome folder inside your Firefox profile folder and then placing a userChrome.css file inside, that includes a custom style rule. The rules you put in the userChrome.css file will override the default styles in Firefox.

Note: Custom style rules might not work every time because of other factors (such as incompatibility with other custom style rules) beyond the Mozilla community's control. Your custom style rule might also stop working each time a new Firefox release comes out.

Here's how to modify Firefox so that tabs are shown below the address (URL) bar instead of at the top:

If your Firefox profile folder already has a chrome folder containing userChrome.css:
Go to https://www.userchrome.org/what-is-userchrome-css.html and copy the CSS rules under the "Move the Tab Bar Below the Other Toolbars" example here into your userChrome.css file. After saving your changes and closing the file, you should turn on your Firefox title bar or menu bar on Windows. (The CSS rules you copied include other suggestions as comments.)

Otherwise, follow these instructions:
(See this help page and our community member's video starting at 8:45 for more information.)

1. Open your currently active profile folder: Type about:support in the Firefox address bar and, under the "Application Basics" section next to "Profile Folder", click Open Folder (Windows) Open Directory (Linux) or Show in Finder (Mac).
   • On Mac, a folder will open that contains your profile folder. Open the selected profile folder (it will be named something like xxxxxxxx.default for a default profile).
2. Create a new folder named chrome inside the profile folder.
   • Create a desktop shortcut to the chrome folder, if you wish, for easier future access.
3. Download the following file and move it into that chrome folder:
   https://www.userchrome.org/samples/userChrome-tabs_on_bottom.css
4. Rename the file, from "userChrome-tabs_on_bottom.css" to userChrome.css
   • Note: If the file you downloaded was missing .css from the file name, that means Windows is set to hide file name extensions. In that case, rename the file from "userChrome-tabs_on_bottom" to userChrome.
5. Restart Firefox, which will discover that file and apply the rules.

Tip: Turn on your title bar, or the menu bar on Windows, after you've made these changes.

Hello MkII,

thank you for your answer but its not my question and I did find those option. But maybe I was not clear enough in my question, sorry.

I want the tabs at the bottom of the screen, not below the other toolbars, but really completely at the bottom of the window/screen

And I can't find any css code for that sadly

Try this one:

   #TabsToolbar {
   position: fixed;
   bottom: -0.5em;
   width: 100%;
   }
   #tabbrowser-tabs { width: 96%; }
   #content-deck { margin-bottom: 2.5em; }

TyDraniu

perfect, thank you very much. I played a bit with the numbers as I am on Linux so maybe a small difference there but its exactly what I was looking for.

thank you very much !

Wow! Thank you!... I just got my tabs back to the very bottom.

Question: What tweak moves the tabs up just a little... like 1/64" as the very bottom of the tab is missing.... Note: using windows 10

Update: I found the line to tweak... changed: bottom: -0.5em; to: bottom: -0.0em;

It is so nice to have my tabs back on the bottom next to the task bar.. Now I have to get use to the new setting, but this is the only way to have it in my opinion. The top is already busy with the quick links and settings ect. and I like the task bar at the bottom as well. To me web sites are like programs/apps and belong next to the task bar. You can go from a program to a web site of your choosing with one click. You just bring the bottom of other programs just above the the tabs. FYI: this is on a 27" monitor..

You may want to disable this feature for Full Screen mode to make auto-hide work and avoid getting the tab bar.

#TabsToolbar:not([inFullscreen="true"]) {position:fixed; bottom:0em; width:100%;}

None of the suggested fixes works with 58.0.2 which just attacked my computer. Any other ideas?

on 58.0.1 (64Bit) Firefox for openSUSE openSUSE - Tumbleweed

and it does still work, would be strange if a .0.x update would break it, but if I ever get 0.2 will let you know