You see the "List All Tabs" button in current Firefox versions if there are that many tabs open that you get the Tab bar scroll buttons appearing.

Add code to the userChrome.css file below the default @namespace line.

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

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

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

Thanks for your attempt, but I want to be able to make an EXTERNAL shortcut to Firefox to open a page (only if it isn't open), which means that viewing them in Firefox is irrevelant.

I better let cor-el answer your question, but I suspect it may not be possible since the fix to Bug 292789 - SCRIPT tags can access chrome .

For any readers of the thread wishing to find open tabs whilst using Firefox it may be worth noting that % may be included in the location bar.

That then filters for matching open tabs and may be useful if you have many tabs not visible because of the number of open tabs in the window, or the use of multiple windows.

• see Address bar autocomplete suggestions in Firefox_changing-results-on-the-fly