I use firefox, I mostly like it, but it still doesn't support chromium style tab groups (no, that one extension is not similar), and its webgpu implementation also doesn't work on most websites more than a year after Google made their version available by default
Not sure if this is “that one extension”, but I use Simple Tab Groups for Workspaces-like functionality, similar to Edge and Vivaldi. I know, it isn't tab groups, but I use it similarly.
I'm guessing, they're referring to multi-account container tabs. It's what the Chrome feature took heavy inspiration from, but of course without the privacy protection aspect.
I've been using Vivalid, they have 'Workspaces' (as its Tab Group analog) which is different but in a way that was a pleasant surprise and kind of reminds me of older systems. Imagine working with one tab group at a time and the rest disappear when you're not on that workspace.
It's chromium based, but it's pretty custom at this point. Chrome extensions are still compatible, but the interface/etc will throw you a bit if you're looking for something that's a direct swap.