FYI.

if anyone has problem the new thunderbird update 45.4.0 trying to start with Lightning calendar and gets the “Add-ons Manager”
tab error message of a missing component, click the “Extensions”
to left.

in Lightning ‘bar’, select [Disable], restart thunderbird, problem solved.

i do not use Lightning calender, so problem was easy to solve.

if you have been using Lightning calender, problem may not occur.