Tabs that haven’t been opened recently should be dumped from RAM anyway. In that case there’s very little difference between a tab and a bookmark. You could use tabs as bookmarks by duplicating one, or you could use an addon to have live bookmark previews and use bookmarks as tabs.
It’s possible to store open tabs into a bookmarks folder, (in at least one browser), so you still have them stored, but don’t have them open.
It’s like taking a picture of something as a momento before throwing it away.
Tabs that haven’t been opened recently should be dumped from RAM anyway. In that case there’s very little difference between a tab and a bookmark. You could use tabs as bookmarks by duplicating one, or you could use an addon to have live bookmark previews and use bookmarks as tabs.