With Flash Player 15, Firefox Now retains focus every time when Flash Processes are Launched.  Two years back, users reported a bug to Adobe related to Flash Player in Firefox on Windows 7, this bug has been fixed by Adobe with the release of Flash Player 15 . The bug 3223393 is: Firefox window loses its focus when Flash Player (version 11.3) processes are launched, which actually shouldn’t happen, all users encountered this.

Adobe Fixes Firefox Focus issue in Flash Player 15

A lot of users, in the bug reported page said they cannot reproduce this with Flash 15 in Mozilla browser.

Flash player version check page firefox

Make sure you’re using the latest version of Firefox and Flash player, and try the below steps, if you can reproduce the issue, let me know or help other users by reporting to Adobe

1. Start Firefox, and start Windows Task Manager in order to observe the Flash plugin processes.
2. Display any web page with Flash content, such as http://www.adobe.com/software/flash/about
3. The three Flash plugin processes (see above) should now be visible in Windows Task Manager.
4. Leave all web pages with Flash content (by going to www.google.com for example) so that no
Flash content is displayed in any tab in any Firefox window in the entire user environment.
5. Wait 180 seconds. The three Flash plugin processes should now disappear from Task Manager.
(Instead of waiting 180 seconds, it is sufficient to spend 180 seconds browsing web pages
which have no Flash content, which can of course happen with a real-world Firefox user. The
important thing is that 180 seconds must elapse without any Flash content being displayed in
any tab in any Firefox window, so that the three Flash plugin processes will be terminated.)
6. Return to any web page with Flash content, such as http://www.adobe.com/software/flash/about
This should cause the Firefox window to lose focus due to process re-launch, as described above.
7. Steps 3 through 6 can be repeated indefinitely, imitating an eclectic real-world Firefox user.

Thus, if you’re using older/outdated version of Flash Player on your computer for Firefox, it is recommended for you to upgrade to the latest version to avoid these sort of issues.