Are we need to remove software, that support patented formats?
If add support of mp3 in firefox is bad idea because of software patents, then it will be logical to remove software, that already have support of patented formats.
Or I don't understand something?
No. Firefox is a web browser that a lot of people use, so if it doesn't support a patented format, that will discourage web developers from using that patented format. Trisquel currently is not a very popular OS, so it isn't able to put pressure on those who distribute audio and video files in this way.
In addition, there is a very specific goal with web browsers that don't support patented formats: to fight against the move to make these patented formats web standards, which is a very bad idea.
No. Trisquel only have free software. Doesn't matter if it is patented or not. If it is free software is ok.
If Trisquel add MP3 in HTML5 with Gstreamer or another free software is fine, no problem. But I always prefer only free-patent formats like PNG, SVG, Ogg, FLAC, WebM, WebP...
Using patent-encumbered formats is a risk (rather than a bad idea) for developers because they may get sued at any moment. It is a risk (rather than a bad idea) for the users because, once that happens to the free applications, the users simply cannot read their files in freedom. That is, they either have to abandon their files or bargain their freedom to read them. Using free software to read/write patent-encumbered formats does not directly infringe your freedoms. It only represents a (real) risk.
If Mozilla would decide to include MP3 support in its Web browser, Trisquel would let it. Mozilla simply does not want to take this risk.
Notice that any program you use potentially infringes hundreds of patents. That is a consequence of the absurdity of software patentability.