It's potentially Flash.
I think you're right.
I went into the mozilla folder within my Everquest II folder and created a file called user.js.
Within that file, I put the following line and saved the file:
This prevents mozilla from scanning for PLIDs which basically means that it won't load the plugins for RealPlayer or Flash.
Once I had that file in that folder, no matter what I tried and no matter how many times I tried it, I couldn't get the game to freeze. And this was without being logged in and ads displayed on the page. Occasionally I would see an ad that had the icon to click here to load the plugin and I don't remember seeing that before.
If that's the case, testing for the in-game browser and making sure not to send it anything with Flash should solve the issue without having to place that file in every users mozilla folder.
This would also explain why it happens for some and not others. If you don't have flash installed on your machine, then the in-game browser won't be able to try to load flash and won't have an issue.
I have no idea if ALL flash causes the problem or if it's just something to do with the Flash stuff coming from Zam or I'd suggest having the game team push that file out to the mozilla folder for everybody's machine. Also, there are several other things you can turn off within that file and there may be players who have turned off even more with that file than I needed to to get Zam to not crash for me. I wouldn't want to overwrite their configuration. So it's probably better to not try to get the game team to fix it.
Does that sound like something that's possible? Filtering out Flash for the in-game browser?