User Agent: Mozilla/5.0 (Windows NT 10.0; rv:73.0) Gecko/20100101 Firefox/73.0

Steps to reproduce:

see https://thunderbird.topicbox.com/groups/addons/T8081af301a914c18-M8ef6f6883f2e399e74bb5800/the-need-to-read-write-files-with-tb68

1. browser.downloads.download: if saveAs is chosen, it throws an error

2. If a prompt (to choose dir + name) is requested, it reports that is not implemented

3. The downloadDir seems to be the one set in FF. In any case, if I choose a directory for saving an attachment, that one is not remembered for downloads. Also, in TB, there is no pref set for the downloaddir (as there is in FF)

it was wrong informatinon on topicbox that the downloaddir is taken from FF. Download uses the directory that is set for download in TB settings. It uses this even if TB settings are set to ask on each.

So changing the download dir is possible but a bit ugly:

set TB not to ask for dir
change dir
set TB back to ask for dir

now download uses the dir that was (re)set - although the option is set not to use that.

Actually, that might be good if th saveAs were working. So one has a fixed dir if saveAs is false, to store stuff.
But the workflow is not really expected: using the dir that has been set in option as not to use.

I see why the file picker is not showing. This line is wrong in the context of Thunderbird.

https://hg.mozilla.org/mozilla-central/rev/e6bcaeecfbbc