I'm being prevented from clicking on any link in any email but a big red screen that says "Advisory provided by Google Safe Browsing."

Please help me get rid of this security block. Went into mail, and the first email I opened was for a petition. But when I clicked on it . . . a big bright red screen that said: " The site ahead may contain harmful programs. Firefox blocked this page because it might try to trick you into installing programs that harm your browsing experience (for example, by changing your homepage or showing extra ads on sites you visit). Advisory provided by Google Safe Browsing." appeared. And I couldn't get to the petition to sign it. Nor can I unsubscribe from sites. Nor can I respond to an email about an upcoming doctor's visit. HELP!!!