So I made another silly extension to cover up the translucent toolbar in Safari because I have no idea how glassy Liquid Glass will be in Tahoe. (It also makes the toolbar gray, so there's more contrast between the bar and the buttons.)
Then I submitted the app to the App Store, and it was rejected because the reviewer couldn't figure out what it does despite my explanation. So here's the direct download: https://andadinosaur.com/frosting/Frosting.zip