Firefox similar to other browsers caches image and web files, and saves cookies (small text file stored on your device with preferences and other data for a specific site) from every website you visit, which helps to improve pages loading speeds when you return to the cached sites.
However, cache data and cookies not always work perfectly, and sometimes this data may prevent websites from loading correctly on Firefox, in which case, clearing the cache and cookies may fix the problem.
Click the setting button on the top-right corner.
Click on Options.
On the left pane, select Privacy & Security.
Under “History”, click the clear your recent history link.
On “Time range to clear”, select from the drop-down menu the time range to clear the browsing data. It’s always recommended to select “Everything”.
Under “Details”, check only Cookies and Cache.
In addition, note that you can clear a number of other browsing data, including browsing and download history, from search history, active logins, offline website data, site preferences.
Click the Clear now button to complete the task.
Once you completed the steps, websites will load as they should, but you’ll notice that they will take longer to load than usual. This is expected, and it’s because Mozilla Firefox has to re-cache the data again. As a result of clearing up cookies, you may also need to sign-in again to some of your online services.
Originally published in February 2017, updated in November 2017.