double-click does not open the default program

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http://askubuntu.com – I installed Ubuntu 12.04, with texlive-full and texworks. When I double-click a .tex file in Nautilus, it pops up a Do you want to run "xxxxxxxx.tex", or display it contents? "xxxxxxxx.tex" is an executable text file. Run in Terminal Display Cancel Run If I choose Display, it opens texworks. How can I make it open without seeing the above conversation window? By the way, is .tex file indeed an executable file? (HowTos)