Text Signing Request window is blank on MacOSX

[minfrin]

When attempting to use crypto.signTextAsync on MacOS Mojave, the attached empty dialog window appears.

The web extensions debugger reports the following:

Loading failed for the <script> with source “blob:null/77744f91-ea5f-5542-8838-ab5fb74437ce”. blank:1
Promise resolved after context unloaded
include.preload.js:546
Promise resolved after context unloaded
include.postload.js:766

[minfrin]

[minfrin]

This is related to #14 - this is a Firefix bug - https://bugzilla.mozilla.org/show_bug.cgi?id=1408446