Hello there @ktsiterip,
I’m really sorry for the late response here!
I gave this a try in my OSX Mojave 10.14.1, also had another colleague of mine working in Windows 10 to give this a try, we both had good results in latest Firefox though.
This could be happening due to a conflict with another plugin or active theme. In order to narrow this down, you should perform a conflict test, meaning deactivating all other plugins apart from Hustle and activating a default theme like TwentySeventeen. Then try in your Firefox browser (prefer an incognito window without any extensions). If it works well, start activating the remaining plugins and theme one by one this time, checking each time how’s Firefox, until you recreate the issue.
Prior to conflict test, please make sure you’re having a working backup on hand, in case you’ll have to restore it. Having a staging environment to safely perform this test, is also a handy alternative.
Warm regards,
Dimitris