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Start Firefox using Troubleshoot(Safe) Mode {web link}

A small dialog should appear. Click Start In Troubleshoot(Safe) Mode (not Refresh). Is the problem still there?

It is possible to drag other buttons and controls onto the tabs toolbar, stealing space from the tabs. Could you double-check in the Customize panel whether a flexible spacer or anything else that doesn't need to be there is using space on your Tabs bar (I do recommend keeping the New Tab + button and the List All Tabs button).

More info on Customize: Customize Firefox controls, buttons and toolbars

Are you possibly using code in userChrome.css to style the Firefox user interface ?

• https://www.userchrome.org/what-is-userchrome-css.html

solved my own problem. had used userchrome to get multirow bookmarks. added a css to get tabs at bottom. problem with this file. deleted last portion this file. viola problem solved. could not determine what was in deleted portion that reduced width of toolbar.

That was very good work. Well Done.

LOOK HERE FOR ANSWER: https://support.mozilla.org/en-US/questions/1365847 Make sure you have width:100vw; property rules.

1. TabsToolbar {

 display: block !important;
 position: absolute !important;
 bottom: 0 !important;
 width: 100vw !important;

}

1. tabbrowser-tabs {

 width: 100vw !important;

I think that 100vw is the percentage of the width(?), hence very important is right.

See:

• https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_blocks/Values_and_units

Well, I deduced/inferred that 100vw vs 50vw was a percentage, the linked url confirms it. Thanks for finalizing the solution. The Ts are crossed and the Is are dotted. QED