Firefox Mobile not on myTouch 3G

Hoping to test out the latest beta of Mozilla’s Mobile Firefox but have a myTouch 3G?  You may be out of luck, while the official builds don’t support the chip in the device, there is an Arm 6 build which is listed as compatible.  I downloaded it and tried to install it, but it wouldn’t install either, despite having what I thought was enough free space available for apps.  Turns out it also requires 13MB space on the SD card (is that feasible?).