So are you using default firefox layouit or userChrome.css edits? If I recall by default the "+" should be there. So unless you can show a screenshot of the URL address bar for others to see where it is at.

1. Not using userChrome.css 2. I have used Firefox since 2004 and think the "plus" was in the early versions as muscle memory goes way back. It seems it disappeared.recently.

See whether it is on the Customise palette. Right-click the 3 bar menu or a toolbar and select Customize Toolbar. If it's there, drag it to the toolbar. If it isn't there either, try pressing the button Restore Defaults at the bottom right of the palette.

https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars

Probably you solved this by now but just in case:

Firefox places the New Tab button on the Tab bar (after the last tab) by default. You can move it to the main toolbar if you prefer (using the Customize feature mentioned by Terry). The thing that makes it confusing is that the New Tab button has a different appearance between the two bars.

My plus sign vanished also. It happened, I think, with version 108.0, which also moved my tabs to the bottom of the screen instead of below the navigation bar where I've always had them and want them to return.

Any advice on getting my Tab Bar back up top, with the plus sign in place?

My plus sign vanished also. It happened, I think, with version 108.0, which also moved my tabs to the bottom of the screen instead of below the navigation bar where I've always had them and want them to return. Any advice on getting my Tab Bar back up top, with the plus sign in place?

Thank you for posting a question here since this is a different issue: https://support.mozilla.org/questions/1399697