In order to speed up web browsing, web browsers are designed to download web pages and store them locally on your computer's hard drive in an area called cache. The cache contains a kind of travel record of the items you have seen, heard, or downloaded from the Web, including images, sounds, Web pages, even cookies. Typically these items are stored in the Temporary Internet Files folder.

When you visit the same page for a second time, the browser speeds up display time by loading the page locally from cache instead of downloading everything again. This sometimes results in less than current versions of web pages being displayed. When the cache fills up, performance can slow down and your hard drive may run out of space.

You should periodically clear the cache and use the latest version of the browser. 

Google Chrome: https://support.google.com/chrome/answer/95582?hl=en 

Firefox: https://support.mozilla.org/en-US/kb/how-clear-firefox-cache 

Safari: https://support.apple.com/en-us/HT204098