Firefox extension which forces Github to open diff pages with w=1 appended, so it always displays the changes without whitespace differences. GitHub has a UI option to hide whitespace diff, but that setting is not saved persistently.
The extension can be obtained at: https://addons.mozilla.org/en-US/firefox/addon/github-whitespace-disabler/
Inspired by Chrome extension which can be found here: kemo/github-whitespace-disabler. Originally authored by @maksimovic.