I have a couple of Firefox derivates on my phone that are only for webapps, for example tumblr.
How do I make it so any tumblr link opens in say Waterfox instead of my default Browser.
In the default section of the setting, Waterfox has the option to open supported links but doesn’t have “Open supported web address”.
You can even achieve the behavior OP wants with URLCheck. You can add an automation that checks the link against a regex and opens it in a specific app, bypassing the browser selection pop-up. You can copy the Wikipedia example from this repo and replace the app with your preferred browser. And if you set stop: true, you can add another automation below to catch the rest of the urls and set a default browser. So you never have to see the browser selection pop-up if you don’t want to.