Clearing your browser cache or cookies can sometimes help resolve issues you experience on websites.
First, a little vocabulary:
Cookies: Cookies store information about websites you visit, such as site preferences or login status.
Browsing history is the list of sites you've visited that are shown in the History menu, the Library window's History list and the address bar autocomplete list.
Cache: The cache consists of temporary files, such as web pages and other online media, that Firefox downloaded from the Internet to speed up loading of pages and sites you've already seen. For example, the browser has stored images found on a website to your computer so it doesn't have to re-load that image every time you visit that site. This can decrease the time it takes to load a page. The downside: information on a website may have changed, and until you clear the cache or reload the page, you won't see the new information.
Under History, select Clear Recent History. A new window opens giving you options for what to clear and the timeframe covered.
Visit the Mozilla Firefox support site for more information and to learn how to clear history/cache/cookies on a schedule
https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox
