Haven't tried this alpha yet, but I played around with an older Version. I also tried the WinMo version and I can tell you that Fennec on Android is much better than the WinMo version. On my HD2(running Froyo) it installed without problems and it didn't crash. But because the UI had no priority over the webpage rendering it wasn't really usable. But I think I read somewhere that in this alpha the UI has priority, so when I can I will give it a try again. But the only reason for using Fennec are the sync features.
HTC Prophet(sold)-->HTC TochHD(not in use anymore)-->HTC HD2 running CyanogenMod(lent to cousin)--> Samsung Galaxy S II running CyanogenMod + Nexus 7