“Old CSS, New CSS,” n.d. https://eev.ee/blog/2020/02/01/old-css-new-css/
“Open UI,” n.d. https://open-ui.org/
“Version 137.0, First Offered to Release Channel Users on April 1, 2025,” n.d. https://www.mozilla.org/en-US/firefox/137.0/releasenotes/
Apparently new Firefox will allow to group tabs. Finally some new feature which was actually requested by community.