Sandcastle code editor turns Firefox white

[mzschwartz5]

What happened?

Since the 1.134 release, on Firefox 143.0.4 (aarch64), clicking the code editor icon in the new sandcastle (now at https://sandcastle.cesium.com/) turns Firefox white - it never loads or resolves in any way.

Reproduction steps

1. Open Firefox
2. Navigate to sandcastle.cesium.com
3. Click the code editor icon

Sandcastle example

No response

Environment

Browser: Firefox 143.0.4 (aarch64)
CesiumJS Version: 1.134
Operating System: MacOS 15.6 (24G84)

[jjspace]

Just copying some info back from the PR.

This issue was caused by the font loading check code I added in #12917. Apparently the FontFaceSet.values() does not work as an iterator in Firefox only.
I tracked this down to an open bug report in the Firefox bug tracker:

• https://bugzilla.mozilla.org/show_bug.cgi?id=1780657
• https://bugzilla.mozilla.org/show_bug.cgi?id=1311198

This error in loading crashed the whole page. It's probably worth looking into some sort of error boundaries to try and prevent the full breakdown of the page. For now we can just iterate on document.fonts directly as I did in the PR.

[mzschwartz5]

We might also want some sort of base workflow tests to ensure changes work cross-browser, so I'm not the only one finding firefox bugs :)