I guess this does not show up in installs with non-debug versions - so it went
unnoticed. When doing "make install" in www/firefox with a debug build of
firefox (I'm investigating how it got broken again for sparc64):

cd /usr/pkg/lib/firefox &&  /usr/bin/env LD_LIBRARY_PATH=. MOZILLA_FIVE_HOME=. HOME=/usr/pkgobj/www/firefox/work/mozilla  ./firefox-bin -register
WARNING: NS_ENSURE_TRUE(NS_SUCCEEDED(rv)) failed, file nsINIParser.cpp, line 51
Type Manifest File: /usr/pkg/lib/firefox/components/xpti.dat
WARNING: NS_ENSURE_TRUE(NS_SUCCEEDED(rv)) failed, file nsINIParser.cpp, line 51
************************************************************
* Call to xpconnect wrapped JSObject produced this error:  *
[Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIRDFContainer.Init]"  nsresult: "0x80004005 (NS_ERROR_FAILURE)"  location: "JS frame :: file:///usr/pkg/lib/firefox/components/nsExtensionManager.js :: nsExtensionsDataSource_getItemList :: line 3473"  data: no]
************************************************************
WARNING: nsExceptionService ignoring thread destruction after shutdown, file nsExceptionService.cpp, line 191


Since ini files surely are not arch specific, I guess this is a problem for 
other ports too ;-)

Martin