Please try the [https://support.mozilla.org/en-US/questions/1315663 solution provided here] and see if it works for you.

If you have run through the check via Firefox regarding set as default and it is ok. https://support.mozilla.org/en-US/kb/make-firefox-your-default-browser If you have checked the Preferences->General->Files and Attachments and there are no settings for http(s) links then check the following: * Preferences->General * scroll to bottom and click on 'Config Editor' * Accept the friendly warning :) Look for the following preferences and if they are set up as 'False' then toggle them to say 'True' * network.protocol-handler.warn-external-default * network.protocol-handler.warn-external.http * network.protocol-handler.warn-external.https * network.protocol-handler.warn-external.ftp Close the advanced preferences/config editor click on link in email - it may ask what browser to use - select Firefox and check the checkbox to have it remember the setting.