“Boycotts are normally pretty useless...”
In the case of Comcast, it is much more than an advertiser boycott. Millions of people are directly paying them hefty cable fees every month. Comcast gives a portion of your money directly to Al Sharpton for his racist TV program. They are simply not a reputable company.
Most people are already boycotting MSNBC qnyway because of the horrible programming and “news” coverage. No additional effort is needed.