Please try using the browser in Safe Mode for a while (Help>Troubleshooting Information>Restart with Add-ons Disabled) and see if the problem persists.
It would be helpful to know which kinds of websites (and how many at once) you're trying to load when the stalls occur. Or does this always happen no matter what's loading or whether anything is loading at all?
'System Monitor reports "null is not responding" seems it is NOT getting proper identification from TenFoutFox. Could this be the cause of the system throwing the SBOD?'