Firefox on XO

[James Cameron]

Firefox-26 from Fedora 18 using yum was built by the Fedora project,
but Firefox-50 downloaded from Mozilla was built by the Mozilla
project.

Firefox-26 from Fedora 18 has different build configuration settings
to Firefox-50 from Fedora latest.  You might compare those settings by
looking at the RPM spec file.

You can find the Fedora packaging files for Firefox here;

https://src.fedoraproject.org/cgit/rpms/firefox.git/tree/ (the current
master branch),

https://src.fedoraproject.org/cgit/rpms/firefox.git/tree/?h=f18 (the
last Fedora 18 build),

Firefox might be rebuilt with these configuration settings changed;
see rpmbuild.

But I don't think you'll be likely to find a recent build of Firefox
suited for Fedora 18.  Everyone else will have upgraded by now.

-- 
James Cameron
http://quozl.netrek.org/