What is common with the reason of this forum ? Nothing, so the next time try to use a more useful forum. This one is for K-Meleon and related subject.
To answer to your question, I think it's like if you put your money in a bank and set the same bank having the full power to manage it. You're then not able to see what they do with your money.
For me, the only way to avoid spywares and virus is to use another OS, Linux for example
Mozilla/5.0 (x11; U; Linux x86_64; fr-FR; rv:38.0) Gecko/20100101 Ubuntu/12.04 K-Meleon/76.0
Mail : alain [dot] aupeix [at] wanadoo [dot] fr
Ubuntu 12.04 - Gramps 3.4.9 - Harbour 3.2.0 - Hwgui 2.20-3 - K-Meleon 76.0 rc