How can I stop Flash from leaving full-screen mode when it loses focus due to a mouse-click in the other monitor?

Install Flash Game Maximizer Firefox plugin https://addons.mozilla.org/en-US/firefox/addon/9631, maximize your Firefox window and press F12.

Try running the browser + Flash in a VM that's capable of full-screen mode - VirtualBox is a popular, free option.

This is a fairly absurd workaround, but it looks like it should work, and this solution doesn't do anything to risk compromising security or breaking your machine.

On my machine it doesn't quite work though - I can switch Flash to fullscreen in the VM, but the video freezes as soon as I do so. However I think this is due to a graphics issue with my VM, since video is choppy on there anyway.

Please comment if this works for you!

One of the comments in the linked bug report thread refers to this Youtube video (?!) giving the following instructions on how to hack the flash dll to workaround this.

NOTE: I know, this sounds like a REALLY BAD IDEA. I haven't tried this (my Flash dll is the wrong version), and it's quite possible that this may have nasty side effects such a introducing a security hole or breaking your system!

If nothing else, back up your dll before trying this.

That said, here's what the video says:

You need a hex editor and Flash player version 10.0.1.28 or 9.0.124.0 If you don't know what a hex editor is, cop out now.

1. Open NPSWF32.dll - it's usually at C:\Windows\system32\macromedia\flash\NPSWF32.dll If you use Opera, it's probably at C:\Program Files\Opera\Program\Plugins\NPSWF32.dll
2. Go to this hex address: Version 10: 0x136340 Version 9: 0xC1487
3. If the number here is 74, change it to EB. If the number isn't 74, you've gone to wrong address, or you've got the wrong version of Flash, so these instructions won't work for you.

Please post in the comments if this works for you.

No abuse though if this causes your computer to catch fire or your dog to explode!

For youtube videos (or other services that have a similar embed feature). Simply click "Share" and "Embed". Grab the iframe URL (https://youtube.com/embed/${video_id}) and navigate to that page. The video will use the full window, then fullscreen your browser.