Use Font Awesome in Inkscape

This link: importing-eps-files-into-inkscape contains a very detailed tutorial on how to do this and it worked perfectly for me. It is based on instructions found at inkscapeforum.com, specifically this quote from eelke:

Inkscape's PS and EPS import now uses Ghostscript instead of pstoedit. If you need to open files of these types, install Ghostscript and make sure the directory with the ps2pdf utility from Ghostscript installation is in your PATH. On importing a file, you will see a preferences dialog, similar to PDF import; for multipage PS files, this dialog allows you to select which page to open.

It works only when you put both links; "bin"and "lib" from Ghostscript in : exc. C:\Program Files\gs\gs8.70\lib;C:\Program Files\gs\gs8.70\bin Start -> Control Panel -> System -> Advanced; Click on Environment Variables, under System Variables, find PATH (or make it in the new..), and click on it. In the Edit windows

That is the gist of the solution. The tutorial in the link at the top of this answer shows how to do this step-by-step with pictures.

The problem described in the question was fixed by Khan Academy by changing all the paths from ./ to /fonts/ (for example ./fontawesome-webfont.ttf changes to /fonts/fontawesome-webfont.ttf). It seems to me that Firefox is unable to read files from the special "dot" directory (which simply refers to the current directory).

PS: The lack of semicolon in the CSS after the last attribute does not cause this problem.

Additional comments:

Your edit about the . prefix is a server issue, not how Firefox handles files. KA were referencing the font files from the wrong location – random

Incorrect! The fonts worked correctly in three other browsers as I had already mentioned in question long ago, which means the fonts were in the correct location. It was clearly Firefox's problem with the ./ path as I explained, which forced KA to move the font files to a new location that doesn't need ./, allowing Firefox to also read the font files correctly. Therefore it is an issue of how Firefox handles files.