For people who cannot use it on macOS Catalina. I found a solution here, https://stackoverflow.com/questions/59543692/failed-to-connect-native-host-has-exited . In other words, download the helper program open_with_mac.py to $HOME/Public .
For debugging, I find it easier to debug with Chrome browser. There is a Chrome version of this extension https://darktrojan.github.io/openwith/