The Online Templates tab will supposedly allow you to easily and quickly access different popular templates online. However, this application is a browser hijacker that will attempt to commandeer your browser search and redirect your homepage to search.onlinetemplatestab.com. Search results will then send you to malicious websites to get money from you or infect your computer further. It may also prevent you from changing your settings back.
Search.onlinetemplatestab.com is usually installed through bundled software without you knowing. Remove it immediately.