Hackollapse by m-coleman

Features:

- collapse entire comment threads from anywhere in the tree
- quickly see how many children a comment has
- hide/show child comments while keeping the parent comment expanded
- customize whether Hacker News remembers that you collapsed a comment

Settings:
Easily toggle the visibility and behavior of the actions.

Change how the collapse action works:
- persist on [-]: HN will remember that you collapsed a comment when clicking the [-] icon, but not when clicking collapse
never persist: HN will never remember that you collapsed a comment when clicking [-] or collapse
- always persist: HN will always remember that you collapsed a comment when clicking [-] and collapse
- off: turns off and hides the collapse action
hide child comments: Toggles the visibility of this action

Note: HN will not remember that you collapsed/expanded a thread when clicking this action

Source: https://github.com/m-coleman/hackollapse