I've seen a couple of people around the web mention that with newer versions of WebKit they have begun getting the following warning in their console when running WebGL apps:
Calling obsolete texImage2D(GLenum target, GLint level, HTMLImageElement image)
Calling obsolete texImage2D(GLenum target, GLint level, HTMLImageElement image, GLboolean flipY, GLboolean premultiplyAlpha)
Things still work this way but obviously having the browser barf out a bunch of warnings is less than desirable. Fortunately a bright guy at http://darkhorse2.0spec.com/ (site is in Japanese) did some digging through Webkit's code and found the "right" definitions, which he lists. For me, I was able to get the errors to go away by changing my code from:
gl.texImage2D(gl.TEXTURE_2D, 0, image, true);
gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, image);
And yes, that works with Minefield too. (Well, technically Firefox 4 beta 1) Of course, this probably only works for me because I happen to know that all the images I'm loading are 32bit PNG's. I imagine that telling it the image is RGBA if you were using a JPEG may not work so well (I'll have to try that sometime soon), so your mileage may vary.