How do I set up Picasa to use a customized web browser / email client / file manager / external image viewer?
You can explicitly tell Picasa how to open the browser you’d like by editing the /opt/picasa/desktop/picasa-hook-urlhandler.sh.template file on your disk. You’ll need to follow the instructions in that file to customize your installation of Picasa for your desktop. Similarly, follow the instructions in picasa-hook-email.sh.template, picasa-hook-filemanager.sh.template, and picasa-hook-mimehandler.sh.template in the /opt/picasa/desktop directory to customize your email client, file manager, and external image viewer settings, respectively.