Due to web restrictions, https://web.telegram.org/ cannot register itself to tg:// protocol. The browser only allows the prefixed version web+tg://. Read the discussion on GitHub: https://github.com/zhukov/webogram/issues/594.

This user-script converts any tg:// link to web+tg://.

It is only run when a document finishes loading, so it won't slow down the entire browser. This also means that any dynamically-created links will be left untouched.

This script was also hosted on https://gist.github.com/denilsonsa/b32ee2957982bfa86a00.