Looking for a replacement for atom-service

I am looking for a replacement for the

Components.classes["@mozilla.org/atom-service;1"].getService(Components.interfaces.nsIAtomService);

I am trying to access the setInlineProperty function however I can not find any information on a replacement for atom-service which seems to have been depreciated and unusable as of Thunderbird 60.0

If anyone has any idea about how to go about accessing the inline property it would be very appreciated. In particular I want to change the font size.

I am thinking that I may have to create my own function for this but If there is one already available it would be nice.