Odd problem with USB tethering: Error 324 (net::ERR_EMPTY_RESPONSE) or Error 102 (net::ERR_CONNECTION_REFUSED)
Sometimes rooting may cause such problems.
The phone says "unrooted" or otherwise, bans some programs, i.e. browser, etc., from functioning properly.
I would suggest to apply a factory reset - of course after having all the back up you may possibly need - rather than flashing a clean firmware.