This problem occurs on the most recent Firefox version, under both Windows 7 and Linux (Lite).
As far as I can recall, the feature has been there since the new add-on regime, which is some time ago now.
It can be seen when you produce a new Speed Dial screen with a new tab, and after it has loaded, slide the screen down a bit, just a few dials. After several seconds, the whole Speed dial screen will load again. And it appears that a URL address entry in the address bar, is locked out until the second load has occurred.
If it was just the one machine I'd suspect some sort of virus, but the exact thing happens on two different machines, under two different operating systems.
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