Hello, As you browse the web, Firefox helpfully remembers lots of information for you – sites you've visited, files you've downloaded and more. Firefox cache temporarily stores images, scripts, and other parts of websites you visit in order to speed up your browsing experience.

In order to clear them please follow the articles.

How to clear the Firefox cache

Delete browsing, search and download history on Firefox

In case of problems loading websites you can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• Hold down the Shift key and left-click the Reload button
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• Press "Command + Shift + R" (Mac)

Clear the cache and remove cookies only from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"