This is a recent regression of the full page zoom behavior, maybe from bug 389720, although this happens on all pages, not just framesets. When you zoom in or out from 100%, the vertical and horizontal scrollbars are cut off or hidden entirely, depending on the zoom level, e.g. at 110%, I see only a very thin vertical scrollbar, maybe a fifth of its normal width, but still usable, and at 120%, the scrollbar is hidden entirely and I can't drag it. The effect is visible at almost any zoom level except 50%, 100%, 150%, 200%. I'm using the slider zoom extension from bug 389628, attachment 274906 [details].
I can confirm it, and I can also confirm it is a somewhat recent regression. Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9a8pre) Gecko/2007080910 Minefield/3.0a8pre By the way, I noticed resizing the window solves it, but also produces the reverse effect: when changing zoom, the display area may then become smaller than the available space (the unused space is left unpainted). Naturally, this can also be solved by resizing the window.
Created attachment 276489 [details] [diff] [review] Patch
Comment on attachment 276489 [details] [diff] [review] Patch New patch coming up.
Created attachment 276496 [details] [diff] [review] Patch v2 Okay, this should work.
Created attachment 277177 [details] [diff] [review] Patch v3 Really fixed version... I guess I accidentally posted the wrong patch.
Comment on attachment 277177 [details] [diff] [review] Patch v3 + float oldWidth = mVisibleArea.width / (float)mCurAppUnitsPerDevPixel; + float oldHeight = mVisibleArea.height / (float)mCurAppUnitsPerDevPixel; constructor casts
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9a8pre) Gecko/2007082411 Minefield/3.0a8pre ID:2007082411 VERIFIED