You can get it from here
http://www.onyx-boox.com/onyx-boox-f...x-m90-firmware
I have just tried the firmware because as jian1 said, they may have improved the browser, which I have been too disappointed.
It seems the browser is a little bit faster, and scribble is more accurate and faster. However, the keyboard becomes a bit less responsive. And I also had problem with gmail. I cleared cookies then I could log in. But then the browser jumped out, then I opened gmail again and it asked me to clear cookies again.
Well, I do not expect much about the improvement of speed, as the limit of the CPU. But I am happy to see that Onyx is trying to make better firmwares.