I knew that it was a kind of spyware, but I didn't even care about that, because it was a great addition and I was really wanted to use it. But moreover, it started consuming a lot of PC`s resources. For example, on only one tab with opened Google start page FF ate 20% of CPU and RAM leaked too much with no end. I investigated a little bit and figured out that was a Stylish's issue. After disabling Stylish everything was OK. Fortunately, there is another great alternative Stylus. It's not a spyware, no CPU/RAM consuming and works brilliantly. Thanks for Stylish, but I can't stand with this anymore, Stylus is my choice now.