The build is very rough and probably not usable for day-to-day browsing—early reports suggest that the loading time is very long, and that page loading is quite slow—but it should provide a glimpse of where Firefox Mobile is headed, how it will render pages and if its novel control scheme is usable on a device smaller than the N810.
The CAB download is available here, but I had no luck launching the app on my T-Mobilized HTC Touch Diamond variant. Let us know about your successes and failures in the comments. [WMExperts via Slashphone]