PHPStorm Xdebug always breaks on first line
Run | Break at first line in PHP scripts
-- try turning it ON and OFF few times. Sometimes it is get stuck in between: showing OFF but in reality it is ON.
If this solves your issue .. then -- http://youtrack.jetbrains.com/issue/WI-17389 -- star/vote/comment to get notified on progress. This particular moment has been fixed since PhpStorm v9.
If you still having such issue (IDE breaks an first line) and the above does not help ... then it has nothing to do with this option/answer and it's some misconfiguration at another place (missing or wrong paths mappings and stuff like that).
You can find the option in Run
menu, it's at the bottom.