This add-on quickly shows some interesting statistics about tabs. For example, the total open count, including inactive tabs. It also shows breakdown by hostname, protocol, and addresses (which is useful because you might have multiple tabs open to the same address without knowing it).

Since I use Dark Mode and Firefox is set to follow the system theme, I had trouble seeing the icon at first because it is just a black silhouette of a tab. So for future users: this add-on installs a button to the right of the drop-down menu which is itself to the right of the tabs and to the left of the minimize button (at least on Windows). I used Customize to move it next to my normal add-on buttons.

Simple but awesome for dealing with duplicate tabs, closing all tabs from a site (bugzilla...), counting tabs and loaded tabs. I've been using it for years (I have 10000 tabs currently)

Very good addon. Exactly as described. Missing one star due to better interface such as warning you before closing more then 10 tabs.

Update Nov 02021: Used it for a further few years and works well. Unfortunately it hasn't been updated in that time but doesn't need to.

A great complement to About sessionstore,

https://addons.mozilla.org/addon/about-sessionstore/

Just one thing caught me by surprise: the need to click alongside (not on) disclosure triangles.

The stats page has no details at all. That's the only draw back.

I was figuring it might be interesting to see what kind of information this would provide. The moment I opened it, I realized how much I had underestimated it. This really does provide me with easy access to information that makes managing my high-tab-load life easier. Thank you!
EDIT: ... and I was still underestimating how helpful this extensions is! It is solving a lot of problems for me - especially ones caused by the change in FF architecture. Thanks again!

Just what I've wanted for a long time.

Provides what is in my opinion critical missing functionality. Makes it much easier to get tab hoarding under control.