Reduce delay before switching views from two to one second. Two is too long.
Disable the automatic revert to the original folder view whenever any new message is copied into any message folder while the drag is in progress. This is no longer necessary in the current architecture of the add-on.
Fix a bug which would cause the original folder view to be lost if the user moved his/her mouse into the folder view title area for long enough for the view to be switched automatically, then moved the mouse out of and back into the folder view title area.

You now have to hover over the view title, i.e., the title to the left of the left/right view switcher arrows, to get the view to switch to “All Folders” during drag and drop. Previously, you could hover anywhere in the folder tree, but that is no longer the case.

This functional change is unfortunately necessary to work around some deficiencies in the drag & drop facilities provide by Thunderbird.