Use Web Video Downloader to download Flash SWF online:
By default, SWF capture function is disabled. To enable it, please select View > Options from the main menu. In the Video Capture page, make sure Flash Movie (*.swf) is selected in the file type list, as demonstrated below.
After the Flash Movie (*.swf) is downloaded, you can right click the file and directly open it with Sothink SWF Decompiler, as demonstrated below.

