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Mozilla Firefox is Working on a Tab Grouping Feature
(news.itsfoss.com)
A place to discuss the news and latest developments on the open-source browser Firefox
There are Extensions to do that if you want.
They require a lot of tinkering for a half-arsed result. Built in vertical tabs like in Vivaldi or edge work and feel much better with just a single setting.
There's a fork of Firefox which have this feature in built known as Floorp which I personally use.