Hazel doesn't close tabs because it's 'like a trip down memory lane.' Mozilla says it has some profile and tab group features coming later this year that might help her organize those memories.
Of course the tabs would just come back up next time they open the browser window again. Can't risk losing those precious tabs, there might be an important one among them.
As a previous tab hoarder, excessive use of bookmarks is the answer. Organized is more useful, but even a single bookmark folder for all of your "I'll need this later" tabs will do wonders for you, and being a bookmark hoarder is so much more functional than being a tab hoarder. You can actual reset your browser every once in a while.
But then I'll have to take an explicit action to keep my tab! I'd much rather have no action required to save that tab that I'm likely to never visit again.
Bookmarks are not a safe way to store links, as I have learned. Every URL can only be present in a single bookmark, and an addon can mess it all up if it decides to create new bookmarks for links that you have already bookmarked. It's location (the bookmark directory) and tags are lost, and if the addon decides to delete the bookmark that it has made, the link itself is lost too.
Yeah, I have a mental cutoff somewhere around 200 tabs. I don't count them, but I routinely so a "close to the right" and get 100+ in the "are you sure" pop-up. I do this about every week or two... And yes, I close a lot of tabs as I go.