Homestuck Companion by Makin

Homestuck Companion displays all existing commentary for Homestuck (up to the end of Disc 2, two thirds through ACT 5 ACT 2), complete commentary for Problem Sleuth and enables keyboard navigation for all adventures on the site.

It also links your browser to the Unofficial Homestuck Collection (https://bambosh.github.io/unofficial-homestuck-collection/), redirecting Homestuck.com links to the appropriate collection URL in real time. You can use the Homestuck Commentary extension (https://homestuck.net/collection.html) to get the ultimate experience.

To see the in-browser commentary: just go to a supported URL like "https://www.homestuck.com/problem-sleuth/10" or "https://www.homestuck.com/story/513" and behold the commentary. Use the extension options in order to disable commentary display, if you just want the controls.

Keyboard controls (arrow keys for changing pages, right ctrl key for opening/closing pesterlogs) work on every page of every adventure except Bard Quest.