The fact that passive mode isn't working is likely my doing. I'm not willing to forward more ports that are needed, so I'm only forwarded ports 20 & 21 so people could connect to my server through non-passive connections. I already have instructions
for my friends on how to get it to work, so that has worked in the past.
The firewall would not be the reason anyways seeing as one of my buddies was able to connect to it through the browser when I tested it earlier today (unsure what browser he was using, however). I forgot to mention that I had already done what you said with the firewall settings, which didn't make a difference.
The problem appears to be with browsers, not FTP clients, so I'm not entirely sure what the problem is there. I've tried changing around my security settings in IE, but so far have not succeeded in getting it to work with my browser.
I will try what you said with deleting the serial in the settings.xml file & will post back to let you know if it fixed the browser-access issue or not.