Review for Provider for Google Calendar by Scar
Rated 5 out of 5 stars
Now working great for me with TB 102.3.2.
Minor issue: Sometimes have to sign in to google account twice before list of calendars show up.
Major issue (solution found): Unable to accept invitations for some accounts. Fixed by exporting/importing calendar in Google directly, see https://github.com/kewisch/gdata-provider/issues/63#issuecomment-1279948080 for details.
To create your own collections, you must have a Mozilla Add-ons account.