On OSX 10.6.8, Thunderbird 38.3.0, why can't I browse to attach a file on a mounted volume?

After just recently updating to 38.3.0, I can't browse to attach a file on a mounted volume. The top of the file browser page shows I am connected as the correct user, but I don't seem to have permission to drill down into the mounted volume. In Finder I can drill down to every file. As a terrible work-a-round I have to copy the files to my Desktop, then attach them, ugh!

Thanks for any help.