Why doesn't it work?

[Darknight1366]

ShellExecute("C:\Program Files\Mozilla Firefox\Firefox.exe") ; Working fine
Winwaitactive("Mozilla Firefox" , "Google")
Send("Wow") ;doesn't work

[lowray1975]

You need to change the WinTextMatchMode or be more exact. The following works perfectly:

Opt("WinTextMatchMode", 2) 
ShellExecute("C:\Program Files\Mozilla Firefox\Firefox.exe") ; Working fine 
Winwaitactive("Mozilla Firefox")
Sleep(5000)
Send("Wow")

More importantly, check out either IE.au3 (included with the AutoIT download) or ff.au3. Both allow you to control the browser via code.