STEPS TO REPRODUCE: 1. Load URL ( http://ftp.mozilla.org/README ) (or probably any page) 2. In a separate tab, visit about:config 3. Set layout.css.devPixelsPerPx to 2 4. Return to the tab with README 5. Zoom in or out (with Ctrl,+/- or Ctrl,mousewheel) ACTUAL RESULTS: Content snaps to a smaller viewport, 1/2 the size of the actual usable area. NOTE: If you set layout.css.devPixelsPerPx to 3 or 4 in step 3, then you end up with a viewport 1/3 or 1/4 of the usable area. NOTE: If you reload the page, everything becomes fixed.
Summary: After changing layout.css.devPixelsPerPx to "N" and zooming, viewport is too small by a factor of N. → After changing layout.css.devPixelsPerPx to N and zooming, viewport is too small by a factor of N
Created attachment 480195 [details] screenshot with layout.css.devPixelsPerPx = 0.5 (In reply to comment #0) > NOTE: If you set layout.css.devPixelsPerPx to 3 or 4 in step 3, then you end up > with a viewport 1/3 or 1/4 of the usable area. This happens in the reverse direction, too. If you set the pref to "0.5", you end up with a viewport that's twice as wide as your window. (This is easier to see if you load something like http://www.mozilla.com/en-US/ , since that URL has more content and is supposed to be horizontally centered.)
Attachment #480193 - Attachment description: screenshot → screenshot with layout.css.devPixelsPerPx = 2
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