Versions for Linux x86_64 and Mac OS X can be downloaded from http://sourceforge.net/project/showfiles.php?group_id=175748
An extension make firefox support Compiled HTML(.chm) file reading.
After install, with "File | Open CHM File", you can open an CHM file in Firefox. With "View | Sidebar | CHM Reader" or press "Ctrl-E", the sidebar which contains topics and indexes listing of the CHM file will be showed.
Open chm file from command line: firefox chm:file:///path/of/your.chm
Open chm from Nautilus: 1. right click on an chm file; 2. Select "Open with Other Application"; 3. Select "Use a custom command"; 4. Input "firefox chm:%U" and click Open.
You can download the latest version from the homepage.