Hea1th-insurance-costs.com Malware

A day or two ago,each time I start up Firefox,Avast says that Malware has attacked my computer.The site's name is Hea1th-insurance-costs.com and I'm afraid I might already be infected,because,as I said it attacks my computer each time i go in Firefox.My start-up page is google and Firefox is my default browser.Please help because I'm really worried.Thank you in advance!