You will only see the List All Tabs button if there are that many tabs open that you get the Tab bar scroll buttons appearing.

• Permanent List-all-tabs Button: https://addons.mozilla.org/firefox/addon/permanent-listalltabs/

• bug 714281 - Show the all tabs button only when the tab strip overflows

You can also Add code to userChrome.css below the default @namespace line.

• http://kb.mozillazine.org/userChrome.css

The customization files userChrome.css (interface) and userContent.css (websites) are located in the chrome folder in the user profile folder.

• http://kb.mozillazine.org/Editing_configuration

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

#tabbrowser-tabs ~ #alltabs-button { visibility: visible #important; }

Doesn't work, though. I overflow and still get no dropdown.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.org/kb/Safe+Mode

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Sorry, I forgot about posting this. I got it working. I just had to restart Firefox after putting the button back up there from the Customize screen. (I'd removed it because I rarely used it).

I have my own work-around for this.

Invoke 'customise' (via right-click on Help, or any unused part of a toolbar),

Unless it's been moved, the tab-list drop-down ▼ then appears, where it should have been, to right of tabs.

Use the grabber to move the ▼ over to the left of all tabs.

Coming out of customise mode, the tab-list arrow happily remains there, fully functional (for me, at least).

It doesn't have to go there, you can even put it in the Add-on bar - just that if you leave it on right of the tab-bar, where it 'should' be, it frustratingly vanishes out of sight when you leave customise mode.

I thought this was a bug, where the length of the tab bar becomes too long & the useful functions vanish to right of screen. It seemed to be related to certain add-ons, but I can't be bothered to track them down.

Presumably the length of the tab-bar is a variable, but it is hidden and not available to be reset in about:config, just to annoy me.

You can see that the CSS code that is used to show or hide the list all tabs button and the new tab button isn't really easy. The alltabs-button should be there there is overflow if it hasn't been (re)moved to the toolbar palette or to another toolbar.

You can open this file via the location bar and scroll to line 16

• chrome://browser/content/browser.css

#tabbrowser-tabs:not([overflow="true"]) ~ #alltabs-button,
#tabbrowser-tabs:not([overflow="true"]) + #new-tab-button,
#tabbrowser-tabs[overflow="true"] > .tabbrowser-arrowscrollbox > .tabs-newtab-button,
#TabsToolbar[currentset]:not([currentset*="tabbrowser-tabs,new-tab-button"]) > #tabbrowser-tabs > .tabbrowser-arrowscrollbox > .tabs-newtab-button,
#TabsToolbar[customizing="true"] > #tabbrowser-tabs > .tabbrowser-arrowscrollbox > .tabs-newtab-button {
  visibility: collapse;
}

@cor-el

I see what you mean :-D

(More of an assembler oriented person, myself.)