I am running latest Thunderbird beta 63.0b1 (64 bit) on Ubuntu Linux (18.04), and emails I receive with ics calendar invitations (themselves created from Thunderbird, although an older version), are not giving me the options to “Accept” the invitation and load it into my local calendar. I just have the normal reply etc options.
This was working (and being used constantly) in all previous beta versions.
Is there perhaps a setting I have accidentally switched off, or is this a bug ?
Update: I have found the ability to add the button “Add to calendar” via the “customize” feature of the display window. This, however, does not interpret the ics data correctly. It puts the ics data in the body of the “New calendar” entry box. By selecting the ics data from here, and saving it to a file, then importing it using “Events and Tasks->Import” I can now get the calendar entries into my calendar, so I have a workaround, but it’s very circuitous …