To install these bookmarklets, copy the line starting with javascript: into the URL field of a bookmark in your browser. For each one, I've included both a one-line version you can paste directly and a formatted version so you can read it. The (function() { ... })() IIFE wrapper in the one-liner is there because that's how you have to wrap up a block of code.
Presumably to optimize initial page load time, GitHub collapses large files in a diff by default. This clicks all the "load diff" buttons on the page. Note that we use a setTimeout to do it a second time 5 seconds later because on very large diffs, the full list of files can take time to load, which means you can click the bookmarklet too early.
Page to try it on: https://github.com/oxidecomputer/omicron/pull/2645/files