Hi I recommend that you have a read of this [https://support.mozilla.org/en-US/kb/applications-panel-set-how-firefox-handles-files?redirectlocale=en-US&as=u&redirectslug=Options+window+-+Applications+panel&utm_source=inproduct article] that will help walk you through how to set a default application. I hope this helps, but if not, please come back here and we can look into a different solution for you.