That is not valid ABP filter syntax. This is what you want:

    *$websocket,domain=~site1.com

For more than a single site:

    *$websocket,domain=~site1.com|site2.com|...

I would personally suggest people to just enable advanced user mode and create rules such as:

    * 127.0.0.1 * blocked

To block all request attempts to 127.0.0.1.