I’ll do some more testing to confirm the workaround issue, and if needed open up an issue. Thanks.
Re support, using the WebGL Report tool it seems like Safari is the only one supporting the extension. As tests are all done on the same device, ie same GPU, drivers and OS, it really does seem like a browser issue. 
There are some subtle details here — different browsers rely on different WebGL implementations (like ANGLE), or different ANGLE backends (like OpenGL, Metal, …), so even on the same device extension support will vary across browsers. But in any case, we probably don’t want this method to fail if it’s supposed to have a fallback behavior! 