Ubuntu file associations

I can not get .pde files to be associated with the arduino IDE. when i go to open with > other, the window that pops up only allows me to set file associations of all plain text files, not ones with extension .pde. how can i do this?

P.S. I've already edited the arduino .sh script to take a filename argument.

Right clic on *.pde > Properties > Open With > Add > arduino

that adds the association for all plain text files, not just *.pde ones.