@Braid
Your H2O (1st gen) is a Mark 5 device. You can manually download fw 4.6.10075 using the the download link in post #1 of this thread.
Instructions for how to manually install (i.e. sideload install) this firmware can be done by following directions in the second-half of
this thread. The part labelled 'Installation Instructions for Direct Zip Files'.
P.S. You do not need to bother doing step 4 (uninstall patches) as a new firmware will automatically remove any previous patches.