Thanks for your feedback.
The screenshot you've posted is from Moodle 1.9 and the Wordsearch app doesn't offer a fullscreen option. Fullscreen is when Flash Player takes over the user's whole screen and it covers everything else, including the browser and operating system navigation and bookmark areas.
Do you mean full browser? Full browser is when the Flash embed window takes up 100% of the width and height of the browser web page display area, i.e. width="100%" height="100%". The browser and operating system navigation and bookmarks are still visible as in the screenshot you posted.
In the SWF Activity Module for Moodle 2.5+, you can set the width and height of the Flash Player window to anything you like, in % or pixels, and in any combination. You can also set the background colour of the HTML web page as well as the background colour of the Flash Player window.
Two advantages of this approach is that it's easy to embed SWF apps into other pages in Moodle using iframes and the page load and run times are much faster, and there's less likely to be laggy, unresponsive behaviour from the page in slower devices, e.g. tablets and phones (Yes, some tablets and phones have Flash Player installed in their browsers).