I think it is something to do with the way you are packaging your code.
I took what you sent me via PM and replaced:
"matches": ["*://*.tinder.com/app/recs"],
with:
"matches": ["*://*.mozilla.org/*"],
so that I could test it without going near Tinder.
I confirmed the extension worked, then zipped up the files using the command line:
zip -r extension.xpi *
And could install the extension as expected.
Would you like me to upload the resultant XPI file to this thread?