Yeah, the issue is the extension address which seems to vary. However, if you try to autofill a site “ctrl sift L” while the extension is locked, then it’ll open a tab with the extension. Try grabbing that address from that tab and using it as the home page. On my personal PC browser it’s:
moz-extension://5e11d5bb-2188-48d7-85d3-0e384e6a334e/popup/index.html?uilocation=popout#/lock