I am interested in how WASM will affect in-browser ad blockers like uBlock Origin that work on a finer grain than merely blocking entire domains. Will they still be effective?

Also, how will WASM affect browser extensions that change the look and feel of websites (like Stylish/Stylus), or the means of interacting with them (like Vimperator)?

These questions all boil down to how much control is the end-user going to have with WASM compared to what they had with the pre-WASM web?