Bug 1043612 - follow-up, fix test to not use em since they convert to different px measurements per platform rs=Gijs

--HG--
extra : rebase_source : 38ccc6667aec9adce7cefd3d9b2308133fc0aacc

browser/components/preferences/in-content/tests/subdialog.xul

@@ -7,7 +7,7 @@
 
 <dialog id="subDialog"
         xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
-        title="Sample sub-dialog" style="width: 32em; height: 40em;"
+        title="Sample sub-dialog" style="width: 528px; height: 280px;"
         onload="document.getElementById('textbox').focus();"
         ondialogaccept="acceptSubdialog();">
   <script>