Well actually a .swf will not contain a .flv. An .flv file is a separate type of container format which can hold video and audio files. If a video file is embedded into the main timline of a Flash .swf, it is no longer a .flv file, it becomes a .swf file. So there is no way that Opera or any other Web browser can "generate" a .flv from that .swf.
If the .swf happens to be a video player, then it will play that seperate .flv video file and if you check the browser cache, you will find both the .swf and the .flv have been downloaded. The Browser has not generated the .flv.
Depending on your version of Flash and the complexity of the .swf, you may be able to "Export" your .swf as a .mov (or .avi). Main menu, File/Export movie/ choose your format. However, that doesn't always work very well if a lot of the display is generated by actionscript.
But, there are a lot of transcoders out there on the Internet which will transcode from a format like .swf to .mov. Just Google "transcode convert .swf to .mov", such as :
http://www.ehow.com/how_5302548_convert-swf-mov.html
not that I recommend that particular one, just to show how easy it is to find them.
Best wishes,
Video Man