The edge cases they cited seem to run counter to this expectation: "At this point, we want to issue a special thank you to the WebAssembly teams at Mozilla and

The edge cases they cited seem to run counter to this expectation: "At this point, we want to issue a special thank you to the WebAssembly teams at Mozilla and Google, especially Alon Zakai, for being so helpful. We did run into a few edge cases but with their help we were able to still make it happen and even improved the Emscripten tool chain a bit along the way." If some percentage of realistic projects run into edge cases that are incompatible with either the spec or between browsers, it violates the whole "write once run anywhere" goal.