It is recommended that you *not* use an iframe in a Finesse gadget, use it only as a last resort.
Some web sites will not work in an iframe. Google, for example, blocks displaying a Google Search page in an iframe.
Just because a site allows itself to be loaded in an iframe now, does not mean it will be supported by the web site in the future.
Running a web site in an iframe is considered poor security, as the containing page could access credentials from the iframe page.
Instead use the gadgets.io.makequest function to access a web app using its REST API.
Note: You cannot display a web page returned via the makerequest as there will be cross domain scripting issues with it.
See the WebServicesSampleGadget in the Finesse documentation page here
the format for gadgets.io.makerequest is:
gadgets.io.makerequest(url, callback, opt_params);
The function fetches content from the provided url and feeds that content into the callback function.
Content should be of type JSON or XML that you then dynamically add to the gadget html.