Hmmm. Could be related to an Avast hiccup, I suppose.
What's Avast unhappy about? Is ZoneAlarm blocking it from accessing the Internet, or is it more serious?
I find that sorting the things that cause errors to appear in the logs can solve a lot of problems. Some errors are just down to poorly written software (like the Jeppesen GPS card writer software, that spawns an error message whenever the PC is started, if the card writer isn't plugged in - even if it's not the day to do the new card). Most can be Googled and solutions found - you're not likely to be the first person to have this problem.
The error log is probably one of the better sources of information about what's wrong, so take a look at anything in yellow or red in any of the logs.
When the browser freezes, can you stop it with Ctrl-Alt-Del, then TaskManager, then Applications, then right-click it and "End Task"? Does Task Manager tell you anything about its status?