push "minVersion" to 19.0
(earlier Firefox versions did not support the "AUTHOR_SHEET" type constant in "loadAndRegisterSheet()", see bug 676054. Therefore the CSS rules for Image/Video Documents do not work since they have the same precedence as the original rules from "TopLevelImageDocument.css" and "TopLevelVideoDocument.css". Hacking around with "!important" to support outdated versions does not seem worth the effort.)

push "maxVersion to 36.0
remove compatibility code (GlobalMessageManager interface name change) for Firefox versions <17
(not needed any more after dropping support for Firefox <19 in previous commit)
Nicer Media Pages 3.0