It works in my Firefox 8 (which is indeed beta). I can't think of a reason in particular, but there was probably something added in Firefox 8 that it needs (eg full CORS support or something)
It looks like WebGL maps have their own GPU exclusion list, or something. I launched Chrome with --ignore-gpu-blacklist and WebGL maps still refuses to run.
We do not have an exclusion list, but we do run a micro-benchmark on your machine to ensure your GPU will be powerful enough to handle MapsGL. You can try upgrading your drivers as well, which sometimes improves performance (looks like intel put out new device drivers for that chip about a year ago)
You could try enabling the "Override software rendering list" option in about:flags, although that is probably the same as the --ignore-gpu-blacklist option.
It was news to me that Safari supports WebGL -- the "Enable WebGL" option was sitting up there in the Develop menu all this time when I've been switching to Chrome for WebGL pages.
Um, Firefox has supported WebGL in release builds for quite a long time now.