Comment 9 for bug 191787

All Mozilla applications in Ubuntu distro depend on libstdc++6. Ubuntu lightning 0.5 depends on it too.
But the lightning 0.7 extension, when you download it from Mozilla webpage is compiled to use libstdc++5 (this is partly binary extension, not only XUL).
This is neither Ubuntu bug nor Mozillas. Just Ubuntu is "too new" and does not include libstdc++5 by default, and Mozilla is "for old ones too", that's why they distribute their binaries compiled to use old library :)

But for Ubuntu: maybe it's not bad idea to install some basic libraries in two versions by default?

Btw: I discovered this when I tried to run SUNBIRD 0.7 from command line. Then I had a clear message, that I lack libstdc++ library :)