Just what EXACTLY is Disabled in Thunderbird 'Safe Mode'?

[BLUE SKY THINKER]

Can't fathom this one (!).

Scenario: My Thunderbird address book contains the standard 'Personal Address Book' and 'Collected Addresses' plus half a dozen extra designated ones of my own.

All of a sudden, on opening, 'Personal Address Book' contents is displayed, but impossible to open all the others (icons showing as normal down the left-hand side). Open Thunderbird in Safe Mode and all works as it should.

My understanding is that Safe Mode disables extensions, plug-ins and themes; is there anything else? The only reason I ask is that, although I have no extra themes, I've disabled all extensions and plug-ins (plus my own userChrome for good measure) and returned it to Normal Mode, but the problem persists. I can only assume there is something else in Safe Mode that I'm not aware of, that could be checked/disabled in Normal Mode (?).

Maybe relevant: exported a copy of address book to LDIF last night, but problem may have been prior to that as I haven't tried to access personally designated books for a while.

Obviously relevant (but don't know the cure): Error Console message on trying to access...

gSearchInput is null
chrome://messenger/content/addressbook/abCommon.js


Frustrating.

Thanks in anticipation.