Pin Tab-Groups by Thomas

This addon makes only sense if Firefox is set to "Restore previous session". (Otherwise tab-groups will be lost after a restart.) And it makes the most sense, if Firefox is configured to open new tabs next to the active tab (instead of at the end of the tab-row). If the steps below are followed, new tabs opened from pinned tabs will then open next to the placeholder tab (instead of next to the pinned tabs).

(Multiple tabs opened in the background will be in the order 321. (Similar to how the addon "Open Tab Next Right to Current" does it for normal (unpinned) tabs.)

To get it to work:
1. Install this addon.
2. Manually create a tab labeled "Your_Placeholder_Name" with the url:
data:text/html,<title>Your_Placeholder_Name</title>
3. Put that name in the addon settings.
(Naming the tab something like "----------" makes it look better in the "List all tabs" drop-down-menu. - If nothing is set "Placeholder" works as default.)
4. Position the Placeholder right after the Tab-Groups you want to have "pinned".
5. (Optional): For better aesthetics: Reduce the placeholder tab to a single vertical line via modifying the userChrome.css with:

#tabbrowser-tabs [label*="Your_Placeholder_Name"] {
min-width: 1px !important;
max-width: 1px !important;
padding: 0 !important;
margin: 0 !important;
background: #808080 !important;
opacity: 0.9 !important;
}


6. (Very Optional): To make the tab look even better in the "List all tabs" drop-down menu:

• 6.1. Use this URL with empty spaces before the line to place it in the center:

data:text/html;charset=utf-8,<title>%E2%80%8B%E2%80%87%E2%80%87%E2%80%87%E2%80%87%E2%80%87%E2%80%87%E2%80%87%E2%80%87%E2%80%87%E2%80%87%E2%80%87%E2%80%87%E2%80%87%E2%80%87%E2%80%87%E2%80%87%E2%80%87-----------------------------</title>

• 6.2. Remove the favicon in front of it with this userChrome.css code:

#allTabsMenu-allTabsView image.toolbarbutton-icon[label*="-------"] {
display: none !important;
}