Testing a Pull Request
On the pull request page, look at the checks for this pull request:
Click on one of the CI checks:
Then, scroll down and download one of the artifacts:
Theses links won't work unless you are signed into GitHub. You can bypass this restriction using https://nightly.link
Go to about:debugging
Click "This Firefox"
Click "Load Temporary Add-on"
Extract the downloaded zip, and choose the manifest.json file inside it
Note: The extension will be automatically deleted when you close Firefox