Indeed. In its default install, Trisquel actually ships free software codecs
for those patented formats. That is why Totem (for instance) plays almost any
video you throw at it.
Mozilla does not want to take the risk to be into costly patent litigations.
That is why its Web browser (and Abrowser, which is based on it) cannot read
patented formats. However, Mozilla is working on using system codecs (rather
than developing its own) to read patented videos from the browser. In Firefox
22, it works on Windows Vista, 7 and 8. GNU/Linux should come very soon
(months).
For the moment, there are extensions to the Web browser that allow to read
videos from many popular sites. I personally use ViewTube and UnPlug (which
is not listed in the Trisquel manual I linked to). They are great.
