There's a file boxee.ttf in the original versions of firmware. Which - by looking at the ttf's metadata - seems to be part of LiberationFont which is licensed as "GPL2 + Exceptions".
The main point that causes boxee to be violation of gpl licensing is exception b:
(b) As a further exception, any distribution of the object code of the
Software in a physical product must provide you the right to access and
modify the source code for the Software and to reinstall that modified
version of the Software in object code form on the same physical product on
which you received it.
In new firmware, boxee.ttf is gone but replaced with 2 other files which are also from Liberation package. + 3rd font file which seems to be commercial offering from same company that owns the copyrights for liberation fonts.