It was an extension to show Google Calendar events in Speed Dial. The flashing window happened every time it refreshed. Thanks everyone. Nervous breakdown averted.

I have. Nothing comes up.

Every time I start Opera (26.0 on Window 7 64-bit), a mysterious window opens in the background and immediately disappears. The Opera icon in the taskbar flashes as well. This also happens periodically while browsing as well. This only started happening during the last week or so. Does anyone have any idea what might be causing this? Thanks.