New module loading changes break loading in Firefox

[josh1248]

After updating to the commit at #2904, the frontend is no longer loading properly for me, but only for my Firefox browser (124.0.2). Everything works fine when I tried loading it in Safari.

These are the network and console logs at this commit:

These are the network and console logs before this commit:

Other things that may be relevant:
-Firefox 124.0.2
-Safari 16.6
-Macbook on M2 chip, ventura 13.5.2
-Python 2.7.18 used for gl build
-backend used = true under .env settings
-I note that this issue occurred while working on my pull request at #2856, which I merged master into.

[sayomaki]

Resolved via source-academy/js-slang#1656