FlashResizer is a Firefox add-on, make Flash movies / games resizable. It adds a nearly-unnoticeable two-pixels-width vertical green line next to flash objects, which what youll use to perform the resize.
Furthermore double-clicking that green line will automatically adjust the Flash element to the browser windows inner width/height.

Requirements:
* Firefox
* SeaMonkey

The license of this software is Free, you can free download and free use this browser plug-ins software.