In https://github.com/muristan/OXcallingVodia you can find both versions: for macOS and for Linux.
The macOS version works with all browsers because the app registers the callto protocol in the operating system, so browsers only ask which application to use for the protocol. Then just select OXcallingVodia.
The Linux version depends a lot on the installed desktop. That's why I chose the path here, that in Mozilla the Protocol handler is created. At the first call, Mozilla then asks for the application to open. Then select the shell script oxcallingvodia.sh You can save this choice for the future. .ut the Protocol Handler can probably register similarly in other browsers like Chrome.
My secretaries have new snom A170 headsets and are very excited about Click2Dial. Click on the phone number in Open Xchange, open the line touching the button on the headset and wait until the called party answers.