Which doesn't detract much from the point: it was a proprietary extension by a specific browser, later adopted by all others.

OK, NCSA was wrong to add those tags to Mosaic without going through standards channels or making them "experimental" and accessible through explicitly temporary syntax. However, I have not seen any evidence (much less the hard proof we have as Microsoft is concerned) that they added those tags with anticompetitive motivation, especially considering that Mosaic predated the browser war.