Firefox allows you to add new protocol handlers (currently I only see two for webcal when I click that link), but the trick is finding a URL on Google Calendar to feed the source URL into. Someone might already have posted the recipe but, if not, hopefully a volunteer can figure one out. For comparison: * Windows Live Hotmail success: [https://support.mozilla.org/en-US/questions/921648 Can't register Hotmail javascript protocol handler] * iCloud failure: [https://support.mozilla.org/en-US/questions/925377 I want to set Icloud Mail as my default email. I've tried but I can't find a way to input Icloud instead of Gmail, Yahoo mail or Windows mail.]

navigator.registerProtocolHandler("webcal","https://www.google.com/calendar/render?cid=%s","Google Calendar");

this string seems to work in the web console when it's entered while you're on google.com: navigator.registerProtocolHandler("webcal","https://www.google.com/calendar/render?cid=%s","Google Calendar");