Thanks Guenter for your response - much appreciated. I apologize if I didn't explain everything clearly enough - I have a tendency to over-complicate things sometimes...
Here are the installation strings - seem the same except for location
TBird:
ReminderFox [2.1.5.5.3] release <'20170625_1059'>
Profile directory: C:\Users\Joe\AppData\Roaming\Thunderbird\Profiles\kw7o894s.default
Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 (en-US)
FF:
ReminderFox [2.1.5.5.3] release <'20170625_1059'>
Profile directory: C:\Users\Joe\AppData\Roaming\Mozilla\Firefox\Profiles\hwbxfwe3.default
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:56.0) Gecko/20100101 Firefox/56.0 (en-US)
Sent you a separate email with 2 attachments - a screenshot, also an export of the calendar. Hope you can figure it out.
Relevant point you should know - I am using RmFX both in FF and TBird - they behave exactly the same - the TBird is new so it has to be the latest software - I got them both pointing to the same calendar file. The attachments are both from TBird since I wanted eliminate any question regarding FF, as I am not using the latest version - keeping the old 56 because of all the BS with the new one!
(side Question re FF - does it update add-ons automatically?)
Thanks again - you can respond directly as you'll see my gmail address on my email,
Dani