Of course, "fast" is very relative. A quick test with 'openssl speed' on my laptop (two years old, power-saving mode cutting performance in half, using one of two cores) shows OpenSSL is roughly a hundred times faster than this library on Firefox.
Which is not to say that getting to this point is not an achievement; JavaScript isn't exactly the best language to implement cryptographic algorithms in.
If you just added support for some primitives (like some sort of 32BitArray or 64BitArray) then you'd probably be able to get within an order of magnitude of OpenSSL.
Which is not to say that getting to this point is not an achievement; JavaScript isn't exactly the best language to implement cryptographic algorithms in.