This is a good thing, but just as a pet peave - why do people keep so many tabs open on desktop web browsers? Every new tab uses more memory. Computers were not designed to have 100s of tabs open. There is no way anyone actually actively uses 100 tabs, and I see people all the time with so many tabs you can hardly even see what is there. There is a thing called bookmarks and folders for storing commonly visited sites on a computers hard disk rather than temporary RAM...

But I do think it is good firefox is adding the capability, as grouping can be useful if done right in moderation. But it's just kind of funny the person asking for the feature admits to having huge amounts of tabs open.