Copyright violations stem from distributing an unauthorized copy of a protected work. Modifying an authorized copy shown to one recipient can't be a violation.

Copyright violations stem from distributing an unauthorized copy of a protected work. Modifying an authorized copy shown to one recipient can't be a violation. User agents are expected to be empowered to transform the data they receive to suit the rendering requirements of the end user. Having a third party perform part of the transformation by supplying supplementary code executed by the user agent doesn't change anything.