Bug 773598 - Add MIME types to script tags in mochitest/browser-harness.xul [r=jmaher]

This fixes an error in Metro debug builds that prevented scripts from using
JavaScript 1.7 features.
bug 828138 - remove nsISelectionPrivate::SetPresShell() r=ehsan
bug 828138 - make Selection::GetPresShell() return the pres shell instead of use an out arg r=ehsan
bug 828138 - remove out arg from Selection::GetPresContext() r=ehsan
bug 828138 - GetCurrentSelection() should return Selection* r=smaug
Backed out changeset b4bd9455a5a3 (bug 820124)
Backed out changeset 78960509f7c3 (bug 820124)
no bug - remove a bunch of extra ';'s to make -pedantic happy
no bug - mark several classes final to avoid warnings about deleting objects of polymorphic type