functions in web dont work in mac

When I design a web presentation (using dreamweaver), I have to test all functions used in the web pages in PC (Explorer and Nets)and in Macintosh (Explorer and Nets). The weird thing is that some functions like opening a new browser window will not work in Mac. I have to change behavior from “onClick” to “onMouseUp” which works sometimes. In some case, switching and setting events to show for older version browser do not solve the problem. What causes the different result in both PC and Mac? How to fix?