Try clearing out your browser's cache/browsing history. When you have done that, close out the browser and re-start it in a fresh session. If that doesn't do it, then do a reset of the browser. It sounds like you picked up something trying to hijack your browser session. Also, run a scan of your system with your A/V software. Check in the settings for the browser to see if there are any extensions or plug-ins that you didn't put there yourself.