TB fails to respond and finally displays "A script on this page may be busy, or it may have stopped responding. You can stop the script now, or you can continue
I get the message below when initiating TB and a unresponsive period ~30 seconds or more. I select to stop the script. It stays unresponsive until the message reappears. I select stop again. It remains unresponsive until after a 3rd iteration at which time everything (email and calendar) work perfectly.
"A script on this page may be busy, or it may have stopped responding. You can stop the script now, or you can continue to see if the script will complete."
Script: chrome://calendar/content/calendar-month-view.xml:864 (This one first two times) Script: chrome://calendar/content/calendar-multiday-view.xml:3452 (This one the last time)
I've seen different :XXXX suffix numbers
Running win10 for several weeks - no previous issues. TB version=38.2.0
Running TB in "safe mode" runs fine but of course no access to Calendar. Calendar synced with Yahoo if that is important. Syncs OK.
Wšykne wótegrona (6)
I should note that I've discovered that after a while it goes into the same scenario of non-response - I assume perhaps when the calendar does its sync with Yahoo?
One other thing ... when I switched from multi-week tab on the calendar to the month tab - happened again but only 1 time instead of 3.
lets try and confirm your suspicions.
On the toolbar 
then 
Select the add-ons tab and disable lightning. use the restart link to restart Thunderbird. Is the problem gone?
You can re-enable after the test.
I disabled Lightening 4.0.2.1 and the problem went away. When I enabled it, the issue returned.
The only other add-on is Provider for Google Calendar 1.0.4. Disabling it (only) had no impact and the issue returned
What remote calendars do you have? Does turning off the offline support help at all?
Are you using the Google birthdays calendar? https://bugzilla.mozilla.org/show_bug.cgi?id=1169062
The only remote calendar is Yahoo. I'm assuming by "offline support" you are speaking of unchecking yahoo calendar from the active calendars? When I do that, it makes no difference
I am not using Google's birthday calendar.