I'm locked into using a wireless router for my Internet connection. My FTP client software, FileZilla, evidently has some sort of passive mode 'port trouble' in maintaining a connection because of an inherent limitiation when it's behind a router. Is this a common problem and is there a workaround?  Would other FTP client software have the same limitation? Any fix? Thanks!

Usually your router doesn't block outgoing traffic.

When using Passive FTP, you don't need to open any local ports, so firewalls / routers usually don't block it. It is uncommon that you cannot use FileZilla.

Anyway, you can use DriveHQ FileManager 4.0, which is native to DriveHQ and has more features than FileZilla. FileManager uses HTTP/HTTPS by default.