Comment 19 for bug 1277972

I can confirm this same bug exists in elementary OS Freya. Alt-tab will bring up the window. I installed Devil's Pie:
sudo apt-get install devilspie

and created a blank file in ~/.devilspie called flash-fullscreen-firefox.ds

I pasted the following script into it:

(if
    (or
        (is (application_name) "Adobe Flash Player")
        (is (application_name) "Microsoft Silverlight")
    )
    (begin
        (focus)
    )
)

and then went to the terminal and started Devil's Pie by typing: devilspie

This seemed to solve the problem for me. I am just going to set Devil's Pie to autostart now.

If it doesn't work for you try changing application_name to window_title and see if it works.

- Jay