Sometimes a web browser caches data, such as an incorrect link to a non existant secure http (https://) version of a web site, especially when developing sites. The following may help in certain web browsers.

Clear Firefox Cache

To clear Firefox cache quickly, do the following:

1. Click on Open Menu
2. Select Library and then History
3. Click on Clear Recent History
4. Deselect everything apart from 'Cache' which should be enough to clear the url cache. Next, click on Clear Now

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