The upstream bug report
<https://bugzilla.mozilla.org/show_bug.cgi?id=1245811> is not about
uBlock Origin. It is about resolving alias names in fontconfig files.
But neither uBlock Origin nor Font Awesome use any fontconfig files. So
these are different issues.
The original extension at Mozilla.org  doesn't include a symbolic
link for Linux. This wouldn't make much sense, since the relative path
to the original file may be different on different distributions. Also,
an extension on Mozilla.org can't require a font package on Linux.
I don't think, that a Firefox extension can actually resolve Linux
they are run by Firefox. So I don't think, that extensions have an
understanding of the underlying file system.
The symbolic link was introduced on your side, possibly by an automatic
system to search for duplicate files and replace them with symbolic
links to their canonical installation paths.
But it just doesn't work in this case. You should replace the symbolic
link with the original font file, and then it works now, and not someday
in Firefox 48.
Just download the xpi file from this site, and open it in Xarchiver. You
will find, that the original extension has its own copy of the font file.
Pkg-mozext-maintainers mailing list