Reproduction steps:
1. Open the user's attached "New Unity Project.zip" project
2. Open the Build settings
3. Choose the WebGL platform
4. Check the Development Build box and press Build
5. Execute the Build in the Firefox browser

Expected result: The build doesn't crash
Actual result: The build crashes with the "RuntimeError: index out of bounds" error message

Reproducible with: 2021.2.0b16, 2022.1.0a12
Couldn't test with: 2019.4.31f1, 2020.3.21f1, 2021.1.26f1 ("BuildFailedException: Incremental Player build failed!" after trying to build the project)

Notes:
- Reproducible only on Linux
- Couldn't test with Google Chrome (RangeError: Maximum call stack size exceeded)
- The issue is not reproducible with a Non-development Build ("InternalError: too much recursion" error that appears when running Build is not related to this issue)

First few lines of the error message:
An error occurred running the Unity content on this page. See your browser JavaScript console for more info. The error was:
RuntimeError: index out of bounds