Where is the button now? Normally, overflow happens from the right end of the bar, so if there's a button you can live without, you could call up Customize and move it further left: Customize Firefox controls, buttons and toolbars.

Does that work on your FIrefox?

you could call up Customize and move it further left

The button is already all the way to the left because my tabs are on the left. I wish I had more control without having to download and setup a thirdparty scripting interface to edit attributes.

Can you attach a screenshot that shows your toolbar customization?

• https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem
• use a compressed image type like PNG or JPG to save the screenshot

You mention the Tab bar, do you have buttons placed on the Tab bar as normally they would be placed on the Navigation Toolbar where that address bar normally would resize automatically up to a certain minimum.