Current Develop is broken in Firefox on Ubuntu Linux

[gunchleoc]

Expected Behavior

The Scratch editor shows up in https://llk.github.io/scratch-gui/develop/

Actual Behavior

The "Something's broken" page shows up in https://llk.github.io/scratch-gui/develop/

The last release (https://scratch.mit.edu/projects/277096470/editor) is still fine.

Steps to Reproduce

Navigate to https://llk.github.io/scratch-gui/develop/ in Firefox on Ubuntu Linux. The same page is fine with Firefox on a Windows 10 virtual machine using the same Firefox version on the same computer.

I tried running both master and current develop with a local npm install and got the same result on my Linux, but there are no error messages on the console, just a few warnings. Console log: scratch-gui-console.txt

I have not tried building the project myself under Windows.

Operating System and Browser

Linux Mint MATE: Linux version 4.15.0-47-generic (buildd@lgw01-amd64-001) (gcc version 7.3.0 (Ubuntu 7.3.0-16ubuntu3)) #50-Ubuntu SMP Wed Mar 13 10:44:52 UTC 2019

Firefox 66.0.2 (64 bit)

[apple502j]

Please give me the browser console error.

[gunchleoc]

Here you go:

Unhandled promise rejection TypeError: "e.asset is null"
    u https://llk.github.io/scratch-gui/develop/lib.min.js:72
    loadCostume https://llk.github.io/scratch-gui/develop/lib.min.js:72
    a https://llk.github.io/scratch-gui/develop/lib.min.js:128
    O https://llk.github.io/scratch-gui/develop/lib.min.js:128
    l https://llk.github.io/scratch-gui/develop/lib.min.js:128
raven.js:55:6
    b raven.js:55
    t lib.min.js:128
    exports lib.min.js:128
    R lib.min.js:128
    exports lib.min.js:128
    <anonymous> lib.min.js:94
    B lib.min.js:94
    f lib.min.js:94

[gunchleoc]

I just gave https://llk.github.io/scratch-gui/develop/ a spin with Chromium and it worked, so the issue is specific to Firefox on Linux.