Code: Select all
\documentclass{article}
\usepackage{fontspec}
\setromanfont[Mapping=tex-text]{Linux Libertine}
\begin{document}
The test: firefly, ``strict'', 1--2
\end{document}

Note 1: Changing the font name to {Linux Libertine O}, or replacing the line with "\usepackage{libertine}", fixes the problem. But I would still like to understand what is happening.
Note 2: The previous note is not valid if one installs the ttf fonts from the Debian/Ubuntu ttf-linux-libertine package - there, the ttf font's name is "Linux Libertine O", so the solution from above will result in garbage - while the original code (using "Linux Libertine") will still result in a text without ligatures. (This is reported as a bug in Debian, but has not been fixed yet.)

Thanks,
Michal