I only did 2 tests:
1. With EN-US Seamonkey 2.33 (German Language pack) Build 20150308222025 (Default Theme) on German WIN7 64bit. Goal was to get the "SeaMonkea deutsch" Sidebar from
working in SeaMonkey, that worked fine.
2. Short test with Firefox 36.0.1, also to test whether contents will be shown, also worked fine.
My suggestion to extend SeaMonkey valid target range has been implemented in AMO, but not in "install.rdf"