Damn, that's another thing about Firefox that absolutely drives me crazy. They implement some feature as an extension, then they include it with the browser by default and just leave the extension there for some reason. It's the exact same thing with Firefox translations, it's integrated into the browser now but they still have an extension https://addons.mozilla.org/en-US/firefox/addon/firefox-translations/
A good way to visualize large numbers of tabs (like with tree or panorama tabs), an ad blocker (Mozilla is supposedly privacy-focused but doesn't have this), and a way to group tabs without having them in containers.
The people I know do nothing of the sort and dodge the question when I ask what they NEED so many tabs for. Some people just think its easier to just have tabs sitting around rather than use bookmarks or accept that they aren't going to read that article they set aside weeks ago.
Just browsing documentation can have me hitting that number of tabs easy. I tend to open stuff in new tabs so I can flip back and forth. Also if I'm searching for error messages I like to open in new tabs so I don't have to continuously go back and forth. I won't kill a tab until I know I'm done with it, I have a tab sleep extension to save resources for long idle tabs. Tab groups are a nice feature that I would love in Firefox to help clean things up, I tend to use new windows and virtual desktops to compartmentalise tasks.