Go to App Store (can be found in Launchpad, which is the rocket in the silver circle in the bottom of the screen) and go to updates, which is at the top of app store, and update your Macbook to the latest OS (El Capitan).
Also install google chrome (https://support.google.com/chrome/answer/95346?hl=en-GB) and use it for your web browser.
These two steps might solve it