Icecat doesn't have H264 support

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I installed Icecat with guix on my Debian 13. It works fine but about:support 
page says H264 decoding is unsupported even though VP8, VP9, AV1 is supported. 
That's why I can't watch videos on nitter or invidious. I can only watch videos 
on youtube! Is the problem on my side? Do I need to install a package?