https://docs.unity3d.com/Manual/webgl-memory.html
Dealing with memory issues
When you see an error related to memory in a Unity WebGL build, it is important to understand whether it is the browser which is failing to allocate memory or if the Unity WebGL runtime is failing to allocate a free block of memory within the pre-allocated block of the Unity heap. If the browser is failing to allocate memory, then it may help to try to reduce the size used by one or more of the memory areas above (for instance by reducing the size of the Unity heap). On the other hand, if the Unity runtime is failing to allocate a block inside the Unity heap, you may want to increase the size of that instead.
Unity will try to interpret error messages to tell which of the two it is (and provide suggestions on what to do). Since different browsers may report different messages, that is not always easy, however, and we may not be interpreting all of them. When you see a generic “Out of memory” error from the browser, it is likely to be an issue of the browser running out of memory (where you might want to use a smaller Unity heap). Also, you may sometimes see browsers simply crashing when loading Unity content without showing a human-parseable error message. This can have many reasons, but is frequently caused by JavaScript engines requiring too much memory to parse and optimize the generated code.
Large-Allocation Http Header
Your server can emit the Large-Allocation http header for your content. This tells supported browsers (currently only Firefox) about your memory needs, allowing them to spawn a new process with an unfragmented memory space, or to perform other housekeeping to make sure that the large allocation succeeds. This can solve issues where the browser runs out of memory when trying to allocate the Unity heap, especially on 32-bit browsers.
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