I have so, so many tabs open. And when I need, I can reorganize in a tree structure and just collapse [other projects] tabs and leave them. Combined with "Auto Discard Tabs", I have hundreds+ of tabs open, with only a half-dozen using RAM. Works freakin' great for me, even on a laptop.

(note, this is Tree Style Tabs along with a userChrome.css hack to remove the tab bar; I'm okay with this tradeoff, normal extensions being able to hide the tab bar sounds like it would lead to issues.)

Makes a vertical list of your tabs in the side panel, and opening links from a page makes a node visually indented directly under that tab. Very nice for grouping tabs in a hierarchy as you descend through links on a topic.

Useful for general browsing and for sites like Hacker News: you can middle click links to interesting comments on the home page, then you can go through them one by one, opening the article (which is another tab one layer deeper), and any other links from there, all "contained" in that tree. You can collapse the tree to save space and resume at a later time. After you're done you pop the stack back to the comments and read, right click and close the whole tree when done and move on to the next article you "bookmarked".

For some workflows it's very nice.