How to switch the 'action' field in an HTML form dynamically

I found this site very usefull for Javascript programmings.

I had a problem with a very simple script. It turned out that the issue was with Firefox not letting to set a form SELECT field to a value, which is nit in the OPTION list. IE allows to do it. I had to put a piece of code to detect the browser type, then add an empty OPTION at the end of the drop down. This way I can set SELECT to empty string. It's an ugly solution, but I had to fix this issue quickly.