Hey! That's good news. Let's see if we can't figure out how to review and then land this patch.
For review, we don't use GitHub, we instead use a tool called Phabricator. Most Mozilla developers work using Mercurial, and so the official walkthrough of the process only talks about Mercurial.
The easiest road for you would be to install mercurial, export your patch from Git, and reimport into mercurial and submit from there -- My recollection being that the inital setup of git being a bit slow.
Having said that, there are a good number of Mozilla developers who work in Git, and so there is a workflow that uses git. I personally am much less familiar with it, but it appears that the GeckoView team has reasonably good documentation of what that looks like.
git-cinnabar is something you'll see mentioned: It's a tool which is able to communicate with mercurial repositories from Git