Copy the address from your web browser.
Then in the 'Insert Hyperlink' box put the cursor in the 'Address' field.
Now Press: Ctrl-V [and the address will paste]
Or have the web browser open at the page [at the hyperlink you want]. Open up the 'Insert Hyperlink' box and switch back to the web browser, then switch back to frontpage and you should find the active web page address has appeared in the address field.