When using Thunderbird for email, when I try to attach files from the local Sync.com folder on my MacBook Pro hard drive, the Thunderbird window which opens to allow me to select the files freezes once I click down into the Sync local folder. It happens nearly every time. This has happened only since I upgraded to OS 10.14 Mojave. This doesn't seem to happen when adding attachments from any other folders. The whole of Thunderbird freezes, and I have to force quit - which usually means I lose all the text in the draft email which I had written. Please can someone help!