FWIIW, I have a Marvell OpenRD[1] system running a "normal" RedHat XWindows environment (have not had a chance to switch it to Ubuntu/Debian yet). It runs great, including firefox.
I got it over a year ago so my memory is fuzzy. IIRC, I got it directly from Marvell as an eval board. My employer actually bought it - I gave the purchaser the web site link and it showed up a week or so later.
[1] http://www.globalscaletechnologies.com/t-openrdudetails.aspx