On webpage that put an visible element on the bottom margin of visible windows (regardless of scrolling position), Handy Screenshot captures this element multiple times, leaving it overlaying the interesting part of document multiple times.
Hence unusable for me, but an additional star because it seems to successfully break not even the 4096- and 16384-, but also the 32768-pixel-limit.

HALF-working addon = does what it says, but NOT if U use a dark theme! Hides EVERYTHING if U have black as your background &/or 'background images' disabled in Firefox. Shouldn't matter! Also, U must hit their button, as there is no right-click option. This conceals & makes things harder when U have lots of buttons with 'rollover' = not all shown @ top of browser.