Make javascript focus code more robust

Need to make jquery.tools.focusfirst.js more robust: Internet Explorer doesn't allow to give focus to a hidden element.
As a consequence, if elem.focus() is called when elem is not accessible, there will be this error

Message: Can't move focus to the control because it is invisible, not enabled, or of a type that does not accept the focus.
Line: 1752
Char: 10

Need to add a condition (maybe only for IE) to check if element is visible before giving it the focus.