The fact that there was such a great number of people using the extension – about 1,044,000 users – was an advantage for cybercriminals. Running the malicious JS code could have enabled the attackers to charge commission from their advertisements, making quite a profit.
You should always pay attention when installing software because often, a software installer includes optional installs, such as this ColdSearch.com browser hijacker. Be very careful what you agree to install. Always opt for the custom installation and deselect anything that is not familiar, especially optional software that you never wanted to download and install in the first place. It goes without saying that you should not install software that you don't trust.