Fails on latest Firefox with IndexSizeError and TypeError: a is undefined issues.

[AlexanderMakarov]

Describe the bug
Fails on Firefox with IndexSizeError and TypeError: a is undefined issues.

To Reproduce
Link to Live Editor: big flowchart with styles
Steps to reproduce the behavior:

1. Just open the link.

Expected behavior
Editor shows flowchart diagram as it happens on Chromium-based browsers.

Actual
It fails with 2 errors in webtools "Console":

IndexSizeError: Selection.getRangeAt: 0 is out of range [content.js:1](moz-extension://4de7173c-6c3a-4c4f-badf-fc01dfb565fc/content.js)
    k moz-extension://4de7173c-6c3a-4c4f-badf-fc01dfb565fc/content.js:1
    C moz-extension://4de7173c-6c3a-4c4f-badf-fc01dfb565fc/content.js:1
    S moz-extension://4de7173c-6c3a-4c4f-badf-fc01dfb565fc/content.js:1

and right after

view fail TypeError: a is undefined
    Immutable 16
        r
        ln
        Tt
        J
        k
        ue
        qn
        Tr
        Nn
        Tr
        ot
        Nn
        ot
        Nn
        ot
        j

("16" here is a number of similar errors).

Desktop (please complete the following information):

• OS: Linux Mint 21.3 Virginia (Ubuntu 22.04) - i.e. latest
• Browser Mozilla Firefox
• Version 138.0.4 (64-bit)

[denisw]

I also get a blank page on Firefox 139.0, although the error is a different one for me:

Uncaught (in promise) Error: https://svelte.dev/e/props_invalid_value

According to the Svelte docs, this error is:

Cannot do `bind:%key%={undefined}` when `%key%` has a fallback value