Hackollapse

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