Hi Peakwolf, I understand that you would like to choose an icon for a pinned tab. In the past there was an add on called ico picker, however I cannot recommend it because it only works with earlier versions of Firefox, not the release version. I do not have an answer for you at this time. There might be another way to customize tabs with an addon.

You can probably do this with code in the userChrome.css file.

Here is an example that works for Gmail.

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

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

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

#tabbrowser-tabs .tabbrowser-tab[pinned][label^="Gmail"] .tab-icon-image {
 list-style-image: url("https://ssl.gstatic.com/ui/v1/icons/mail/images/favicon5.ico") !important;
}

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