As of this date this extension for Firefox appears to be broken in Firefox 86.0 in Windows10. The Aspera help file suggests that in a 'certain browser' it may not be functional, and that by switching to another browser you will be able to use the upload function on the Aspera console web page. Sure enough switching to MS Edge allowed the functionality. I am not sure what to guess the problem is with FF and Aspera.

Why need this add-on AND desktop app?
Whats wrong with HTML5