One could make a button to copy the selected url and place it in a tiddler, then have your “MyButton” get the URL as needed from there, this will allow you to keep using the same url, until you select another.
Hi @tw-FRed,
I started from scratch with an empty wiki (https://tiddlywiki.com/) and imported MyButton.json.
→ it works fine
After installing CodeMirror 6 — v0.10.8 the error is back:
Thanks to all, who tried to help me! 
Hi @BurningTreeC,
can you support me please in this case and fix the issue in CodeMirror?
Thanks you,
Stefan