The issue on Firefox 81 seems to be a z-index issue with the edit toggle button....

dubcanada on May 12, 2021 | parent | context | favorite | on: Show HN: Mmm.page – Drag and drop personal website...

The issue on Firefox 81 seems to be a z-index issue with the edit toggle button. Setting it up a 100 fixes it. On Firefox 81 the z-index seems to be calculated to z-index: -2147483648;

Is there a particular reason you are using a 1 year old version of Firefox?