Later when I search for it in address bar and Firefox offers me to jump to one of the tabs, I do that and instantly see related tabs to the left and right of the current tab. My current tab may not always be the exact one I was looking for, but the one I need is still easilly trackable.
If I don't do that and try searching the web my search may not be precise enogh to bring the needed page.
Overall, it's just a different mode of browser use. It suits some people and doesn't suit others. Good thing that Firefox can accomodate both types of users.
If they would improve bookmark-handling it might be a different story. I thing it would probably not even so hard doing this. There are already many addons implementing significant improvements on certain parts. Just combining them and streamlining the whole stuff might be enough.
As a tab hoarder, I have wondered why I do this so many times. I think the answer is that Firefox's bookmarking is ... not great. It is always slow and clunky-feeling to use. You're forced to put these bookmarks into a tree structure, which isn't awful until you realize that you have to remember just how you stored it later. Just for reference, I often find myself running SQL commands against Firefox's places.sqlite DB to locate a page I visited.
I think tab hoarding could be greatly reduced by a series of thoughtful improvements to bookmarking.
When developing, I'll open a new window and keep some tabs relevant for what I'm working on. Frequently it involves me piecing together bits from different APIs or parts of APIs, so require switching between multiple tabs. Often I'll have to come back, and it may take a day or two. No need to keep the tabs running, I just want to quickly pick up where I left.
Stuff like that.
Why not keep it as a bookmark? I don't understand why people live inactive tabs open.