I installed macport following the guide. http://afitnerd.com/2011/09/06/headless-browser-testing-on-mac/
However, when I try to run
sudo port upgrade
it has error message
Can't map the URL 'file://.' to a port description file ("Could not
find Portfile in /Users").
Please verify that the directory and portfile syntax are correct.
To use the current port, you must be in a port's directory.
How should I switch to the right directory?
sudo port upgrade tells MacPorts to upgrade the port defined by the Portfile in the current directory. It's usually a command only developers use while writing Portfiles. The guide likely meant sudo port upgrade outdated instead to upgrade all non-current ports. Since you don't have any ports installed if this is your first MacPorts installation, you can safely skip the command.
Note that firefox-x11 has meanwhile been removed from MacPorts because it was broken, outdated, and nobody stepped up to maintain it.
