There is nothing terrible about the code, it is just missing a couple things.
The problem with what you have now is that you are essentially adding two event listeners to the stage/main timeline, so when you click anything you trigger both functions, but only one of them can ultimately win (probably the last executed).
Select the button for the first set of code that you show and in the Properties panel, assign it an instance name where it says "<Instance Name>"... let's say you name it "page4Btn" Then change your first line of code to be...
page4Btn.addEventListener(MouseEvent.CLICK, fl_ClickToGoToWebPage_4);
Then repeat the process for the other button, using a different instance name for the button.
