Instagram and other social networking apps can be considered a web browser since you use it to browse instagram.com, view, edit, and post images to Instagram like the website version of Instagram, and you need an internet connection to use Instagram like how web browsers need an internet connection for it to browse the internet. But, the Instagram app limits users to only browsing Instagram.com, and you can't use it to browse other sites like web browsers.
I sometimes use my mobile web browser on my tablet as a music player because I listen to a lot of music on YouTube, Soundcloud, and streaming sites. Some of those lyric videos and AMV/Animated Music Videos with video game and anime cut scenes are pretty good.