This is the single add-on that is keeping me on Firefox. Kept me here for years and I can't live without it :)

Can't imagine using Firefox without this add-on. Great work!

So good I even remove the default tabs with some CSS tweaks.
Those complaining of lag you should try something like 'Auto Tab Discard' to unload tabs from memory if you want to have hundreds open for some reason.

Thank you for this.
Best tool to arrange tabs imo.

Developers respect privacy and permissions guidelines by only requesting those ABSOLUTELY NECCESARY when installing. No full Website data request on install. Read only permissions by default.
Friendly side-bar interface automatically groups your tabs by host/path. A no-brainer add-on for Devs, hackers, and the casual internet user. Thank you, piro_or.

Simply amazing. I love how customisable it is!

非常nice

Wow. This thing is seriously awesome. Why this is not how ALL browers are by default is baffling.

Edit: And it turns out to be better at navigating and managing bookmarks better than the actual bookmark manager.