Hey everyone, first comment in this repo, so wanted to give you a big "Thank You" first for creating this great extension!
What do you think of the following small tweak for pull requests:

Alternative implementation ideas:
Why? My team is currently in the habit of manually going through all outdated comments to make sure they were implemented correctly. Sometimes those comments are outdated because of code formatting or similar. We are currently using JS via a bookmark to achieve that functionality, but it would be really nice to have this in this extension.
Very happy to try implementing this myself, but I wanted to check if this is something you might be interested in.
I find myself doing this often too. I feel that we should tackle this and other similar toggles via keyboard shortcut, eg cmd+click=toggle all. No UI clutter necessary.
Alternatively it could be alt+click to match macOS’ alternative behavior, and perhaps we could show the alternative actions while alt is held down i.e. all Show outdated become Show all outdated (macOS does the same)
i also works in the discussione tab? I’m away from keyboard nowI didn't find anything and I think that Github doesn't provide that feature
Here's a screenshot of the shortcuts displayed for the discussion page

JS bookmark for recent Github redesign:
javascript:Array.from(document.getElementsByClassName('outdated-comment')).forEach(l => l.setAttribute('open',true));
@laurenbrandstein thank you!
To add to @laurenbrandstein solution, this worked for me
javascript:Array.from(document.getElementsByClassName('outdated-comment')).forEach(l=>l.setAttribute('class','file js-comment-container has-inline-notes'));
@mgoveas I think the entire conversation needs to be unhidden and I have a few PRs where I have to meticulously scroll around to find these "hidden items" and click a few times and it is a pain.
2020 edition.
Open all resolved:
javascript:Array.from(document.getElementsByClassName("js-toggle-outdated-comments")).forEach(l => l.click());
Click all "Load More":
javascript:Array.from(document.getElementsByClassName("ajax-pagination-btn")).forEach(l => l.click());
thanks @voppe that worked!
The solution for "Load More" is too simplistic that only works for one level (I have PRs that nest at least 10 levels), so here is my better solution: https://stackoverflow.com/a/62711702/95750
There are other solutions that I found later:
Most helpful comment
JS bookmark for recent Github redesign:
javascript:Array.from(document.getElementsByClassName('outdated-comment')).forEach(l => l.setAttribute('open',true));