you appear to be the only one who has reported such behavior.
Some things you could try.
Uninstall FLASH http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-mac-os.html
Uninstall Silverlight https://www.microsoft.com/getsilverlight/get-started/install/removing-silverlight-mac.aspx
Check the Add-Ins/Plugins folder of all your browsers.
As a last note, never, ever, consider installing MacKeeper on your machine.
iMac and OS 10.9.4. Suddenly all my browsers, Safari, Chrome, Firefox are almost unusable because every other click opens a new ACTIVE window or tab trying to sell me something. Any click, anywhere on a page triggers this interruption. Also, small videos automatically open at the bottom of the window I'm using, again selling something. Most of the new windows/tabs are for MacKeeper, but they are for other businesses too and are very sophisticated. If I'm on a site selling cigars, a competitor's window will open with very similar cigar offers and/or products already selected. It happens even when clicking on things like 'shopping cart' or "submit order". This can be misleading to say the least, and dangerous as you expect a new window and get one. My virus program hasn't found anything. I have pop-up blocker on, and I've dumped all cookies. It is getting worse and there are also these "you're the 100,000 visitor" small windows that appear, can't be closed, and actually block things like 'one click' ordering or 'view invoice' at Amazon. Any help? This is making browsing impossible. It happens at all sites, but Amazon is the worst. Tonight there appears a "short (Amazon or hp) survey, valuable prize" window with almost every click, it has horrible voice over, and no close button. I'm being driven crazy. This can't be just me that's been attacked. There must be someone who knows what this is and how to end it. If Amazon is listening, this will definitely hurt your business, and I wouldn't buy MacKeeper now with a gun to my head. Please don't tell me this is just normal Google ads at work. If it is, internet commerce is dead.