Midori usually is fine - it's just that the Midori in the old OpenEmbedded version we currently use is crashy and buggy.
Should change when we update to a more recent OpenEmbedded version, DJWillis is working on that, but he's got little time and there's much work to do.
FireFox and Chromium both eat 30 - 50MB on the NAND, no idea where we should get that space from... we'd probably have to sacrifice stuff like python or some needed libraries...
I'd say we try to upgrade to the next OpenEmbedded version and include a stable Midori that starts up within seconds as it is only a couple of MB big.
FireFox and Chromium can easily be used as PND.