file has to be named applicationFeed.json when putting it there. But, I don't think it'll get that far to read it, as the awesomeplete section is running.
Things to try.
Different browser
on the flash drive, rename (temporarily) the folder /config/plugins/dockerMan/templates-user to something else
Bypass / remove the pfsense box to see if that is it.
Failing that, do this
rm -rf /tmp/community.applications
The load the Apps tab
After two minutes when it fails, post the output of
ls -ail /tmp/community.applications/tempFiles
and probably upload this file to me
cp /tmp/community.applications/tempFiles/templates.json /boot/templates.json