OK, I have had this problem for some time on a Win7 PC and it seems to happen when I restart Tbird for one reason or another during the day. However, if I can start it up after it has been off overnight and leave it running all day, the issue rarely occurs - unless after an update, which is why I tend not to update!
The other day, somehow, an update was downloaded. Having got fed-up of the constant nagging to install, I let it. Big mistake!! The update was to 68.6.0 but when that proved unusable, I took it further to 68.8.0. This was equally unusable, in that every I couldn’t even scroll down a list without it ‘not responding’ for ten seconds. Typing a one sentence email took five minutes - yes you read that right.
So off I went down the rabbit-hole of “things to try”. I rebooted the computer in various modes, no help. I spoke to my virus software company and tried some more things - nothing. I’m sure you’ve all been there.
Finally, on another hour-long trawl of ‘try-this’ links, I came across one that suggested turning off windows search - which made some sense. But windows search was already turned-off in Tbird, so I tried turning it off globally. Still no good, so I turned it back on again on the PC.
Then I noticed below that checkbox in the ‘Advanced>General>System Integration’ area that there is another checkbox entitled ‘Enable Global Search and Indexer’. This had always been checked, so I unchecked it and restarted Tbird.