Does the grey window appear in safe mode (hold Shift when launching TB)? Check if the Remove Duplicates add-on is incompatible or needs to be updated.

https://support.mozilla.org/en-US/questions/1312656

I have removed Remove Duplicates and all the other extensions which no longer worked. I can open in safe mode but the two options do not solve problem. I have restarted computer but still get the same message but it no longer refers to the Remove Duplicates extension. I presume I now have to set up a new profile. Very appreciative of your efforts. Thanks.

IanH, How have you managed since your last posting?