You can search specifically for open tabs in Firefox and probably most other browsers (enter % [keyword] in Firefox' address bar). If you tend to have related tabs near it, it's less work than opening all those tabs back up through bookmarks or history.

I don’t generally find any tab. I work with the set related to my task then close them. The tabs for the previous task are right there, so I can just continue that task until completed, then close those tabs.

It partly works, but I don’t always close tabs for interruptions and aren’t always able to work my way back to uncompleted tasks, so it builds up.

I want to start using workspaces or tab groups to improve my discipline but haven’t yet

Edit: and yes there are times when I don’t remember I started a task or can’t find my set of tabs so open a new set.

And no, multiple windows was a horrible idea. Instead of making it easier to organized tab sets, it made it easier to open many more tabs

Why not just close them and open them back up later?

Because that's extra steps for no actual improvement.

I close the tabs that I'm done with and add new ones when I want to not forget to look at something a bit later.

That doesn't need the "permanence" of a bookmark. (And, obviously I know editing bookmarks is a thing, but that is also extra steps for something I'll only want once in about 15 min from now)