Pin Tab-Groups от Thomas

This Addon 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.

(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 "Placeholder" with the url:
data:text/html,<title>Placeholder</title>
3. Position the Placeholder right after the Tab-Groups you want to have "pinned".
4. (Optional): For better aesthetics: Reduce the placeholder tab to a single vertical line via modifying the userChrome.css with:

tabbrowser-tabs [label="Placeholder"] {

min-width: 1px !important;
max-width: 1px !important;
padding: 0 !important;
margin: 0 !important;
background: #808080 !important;
opacity: 0.9 !important;
}