On GitHub, I often find it difficult to filter out the PR comments which still need to be addressed from ones which won't be addressed (or are purely converstional).
This is a simple Chrome extension to add a collapse/expand button to conversations in the "Conversation" tab on a GitHub pull request, exactly like the button already shown on "outdated" conversations.
Simply click the button (or header text) of a comment thread to collapse it.
Check out this repository, enable extensions "Developer mode", and drag the folder into the extensions page.
This is based on Matthew Robinson's Github-Collapse-Diff extension. (I'm not usually a web developer ;))