User Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:20.0) Gecko/20121213 Firefox/20.0 Build ID: 20121213030751 Steps to reproduce: This happened since the landing of bug 819725. 1. Set layout.css.devPixelsPerPx to -1 2. Go to the Control Panel and set the DPI to 150% 3. Go to any page on the Web with a plug-in. For example: http://www.bbc.co.uk/news/uk-20721117 Actual results: The plug-in is out of alignment with the page.

Yes, I can reproduce the same issue with non-100% DPI on Windows 7, too.

AFAICT, the issue here is that the display-to-device pixel scaling from bug 819725 shouldn't be applied to child/plugin windows, because the move/resize methods for these will be called with coordinates (from their parent window) that are already in device pixels. So we only need that scaling for toplevel/dialog/popup windows, where the parameters are global display pixels. With this patch, the plugin stays in its proper place within the page.

Tryserver build is available at http://ftp-scl3.mozilla.com/pub/mozilla.org/firefox/try-builds/jkew@mozilla.com-f05922d64299/try-win32/.

(In reply to Jonathan Kew (:jfkthame) from comment #3) > Tryserver build is available at > http://ftp-scl3.mozilla.com/pub/mozilla.org/firefox/try-builds/jkew@mozilla. > com-f05922d64299/try-win32/. I can confirm it works. :)