If you are interested in grouping the tabs, have a look at this addon:

https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta...

It allows you to use your tab-list in a hierarchical way, sort of like a filesystem. I group things under obvious roots, and then collapse it till needed.

ctrl-shift-e should open a canvas like area where you can group tabs. Similar to a file folder, I prefer it to bookmarks

Interesting, but seems to be very basic. I still prefer using a wm. I can use different layouts, group windows into hierarchies, display them side by side, take advantage of tiling, use workspaces and have configurable keys for each of these actions. You know, functions that a wm is built for.

And I can always switch to a different wm altogether if I'm not comfortable.

Once you get used to the tab groups they can be very powerful. I use them for contexts myself; one for casual browsing, one for development for client x, one for client y etc, one for research, and the list goes on.

Obviously you can easily achieve the same thing in separate windows as well, so ultimately I suppose it doesn't make a huge difference, but it's the way I find makes for the biggest difference in separating workspaces.