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...and finally, it turns out this thing is browser dependent on my Windows 8.1 machine: Happens every time using Chrome (Version 45.02454.85 (64 bit); doesn't happen at all using Internet Explorer 11
I can't actually read anything in those screenshots, but you're saying it's video ads that appear to "take control of your browser"?
Greenie just got me again and I am running Firefox on Linux Mint.
I will try to capture the frame information when it happens again.
I'm on vacation, and done attending to this for today.