Google Calendar links to ICS de Axel Leroy

Why does it ask permission for calendar.google.com?
In order to intercept event creation URLs, the add-on must request permission to Google Calendar's domain. Because it only requests permission to intercept requests, it cannot read Google's response nor the content of the page.

On Android, Google Calendar links directly open in the application
You probably have set up Firefox to open links in applications. You can change that behavior in the settings, under "Advanced" → "Open links in apps". Select either "Ask before opening" or "Never".

On Android, Firefox asks me to open the link in Google Calendar
That is because Firefox detects that the Google Calendar app can open links to calendar.google.com before the add-on can intercept the link. Simply click on "Cancel" and it will ask you to download the ICS file.

The add-on did not create an ICS file and simply showed me the Google Calendar interface
This is either because the creation URL was invalid or that you stumbled on an edge-case that it does not handle (yet). In any case, create an issue with the URL that failed and don't forget to redact sensitive information from it.

The ICS the add-on created is invalid / not recognized by my calendar application
Please create an issue with the original Google Calendar URL (Right Click → Copy Link), the generated ICS file and the calendar application you use. You may want to edit the URL and ICS file to redact sensitive information beforehand.

Importing each ICS file manually in service X is a chore, why doesn't the add-on do it for me?
To be honest, I originally intended for this add-on to automatically import the generated ICS files into Proton Calendar, but quickly elected not to, for the following reasons:

• It would make the extension significantly more complex.
• Every single change in the import page could break the feature, meaning more maintenance.
• If it ever supported service X, I would certainly be asked to add support for services Y and Z as well.
  My advice then, is to use a calendar application (like Thunderbird or Outlook) and set it up to handle ICS files.

Why doesn't it work with Proton ICS Auto-Importer?
As it is, Proton ICS Auto-Importer only works on direct links to ICS files. Because Google Calendar links to ICS does its work after the user has clicked on a link, Proton ICS Auto-Importer cannot detect the generated ICS file.