unity is not opening script in new tab of flashDevelop

hello
here i have tried unityDevelop,flashDevelop editor for scripting my game
if am double clicking on the script from my project view file is suppose to open in linked editor.
but every time new instance of editor is being opened.
i m used to see files in tab but here i m really irritated coz of this…

Go to FlashDevelop directory, something like: C:/ProgramFiles/FlashDevelop and find a file called .Multi. Remove this file (and maybe take a backup before) and you problem should be solved.