how to overwrite default system key mapping in vim

I want to map f1 to create a n开发者_运维百科ew tab so I add the following line

   map <F1> :tabnew <CR>

into my .vimrc and save it . But when I hit f1 in vim the GNOME TERMINAL MANNUAL window pops up rather than a new tab being created . So what should I do in this situation ?

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Go to Edit | Keyboard Shortcuts... and remap or remove the shortcut.