There was a lot of back and forth [0] over this back when Firefox added support for system libraries. The FOSS purists only wanted to support codecs they could

There was a lot of back and forth [0] over this back when Firefox added support for system libraries. The FOSS purists only wanted to support codecs they could include in Gecko (long before OpenH264) while the pragmatists wanted to make a useful web browser. Support for system libraries first appeared on mobile platforms because it was essential. At the time (ca 2011/12) the likes of YouTube and Vimeo were only delivering MP4 to mobile clients. The purists seemed to think that somehow if Firefox held the line on (likely but not guaranteed) unencumbered formats/codecs that every content producer would see the light and go with those objectively worse codecs with no hardware acceleration for video content. This completely ignored the fact that Flash was common on desktops and supported encumbered codecs just fine. It was in fact the primary delivery vehicle for them. The NPAPI content hole let the purists be intransigent while actually using content on the web. They were also ignoring the design of the HTML5 video tag that encouraged inclusion of multiple source formats and some sort of fallback including object embeds. As for Microsoft they were still pushing the various Windows Media codecs as the One True Way in the Windows XP and Vista eras. They had to support MP4 with Windows 7 because every smartphone and most stand alone cameras were capturing video in MPEG-4 codecs if not file formats. [0] https://groups.google.com/g/mozilla.dev.platform/c/-xTei5rYThU/m/DkM9AIbkNNIJ https://groups.google.com/g/mozilla.dev.platform/c/-xTei5rYT...