I used to have a "diff" command in the Synchronize checklist -> Commands -> Diff, but it's not there anymore. I updated from a version I don't remember (I just overwrote the winscp.exe). However I can't seem to be able to add it there either because:
Synchronize checklist -> Commands -> Customize... button does nothing
See the attached image of the button I press. I'd like to add the diff command back there, but since the customize... button does not work I can't find a way.