Unity has benchmarked its WebGL implementation on different browsers and found that Mozilla Firefox and Microsoft's Edge offered the best performance while Internet Explorer 11 was a distant last and Google Chrome fluctuated in-between.
Jonas Echterhoff from Unity performed the benchmark and found that:
• Firefox 42 64-bit is currently the fastest shipping browser in most of the benchmarks. The 32-bit version of Firefox is noticeably slower than the 64-bit version.
• Edge, as a new contender in these benchmarks comes in second, with results close to Firefox (and actually faster the Firefox 32-bit) in most benchmarks. In benchmarks which stress WebGL rendering performance (Particles, Asteroid Field), Edge performs best of all tested browsers.
• Safari delivers performance comparable to Chrome, up from a year ago when it was significantly slower than Chrome.
• Internet Explorer 11 is far behind the pack in just about everything, and is too slow to be of much use running Unity WebGL content.
• Looking at load times, most modern browsers are able to load the benchmark project in between 5 and 7 seconds. Firefox is able to cache asm.js compilation, which brings subsequent loads down to 1.5-2 seconds.
More details and individual test results can be found on Unity blog.
You can also run the benchmark in your browser directly here.