You can possibly use "Clear Recent History" (Ctrl+Shift+Delete) to clear the cache.

• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

Note that always the full cache is cleared. You can't clear the cache for just one website (domain) like you can for cookies.

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.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)

You can "Remove the Cookies" for websites that cause problems if you do not want or need to delete all the cookies.

• Options/Preferences -> Privacy & Security
  Cookies and Site Data -> Manage Data

Thanks for the reply, but this does not answer my question. I have already mentioned that “reload doesn’t do it” including shift-reload, and I do not want to clear any history, just the cached web page items. The problem occurs when you upload a changed image file with the exact same filename and size that is accessed dynamically by a php “include” within the page. You can shift-reload until you’re blue in the face, but the old image keeps appearing. Only if you Clear Data, but remember to untick the Clear Cookies option first, does the image actually get reloaded when you refresh the page. There must be a config item somewhere that determines the default status of those tick boxes... Dave

firefox286 said

When I need to clear the data cache to correctly display changed web pages when just reloading doesn't do it, the Privacy and Security option to Clear Data has two checkboxes, Clear Cookies and Clear Web Content. I almost never want to clear the cookies, only the cache. The default settings are that both boxes are ticked. Can I change something in About:config that will set the Clear Cookies checkbox default to be un-ticked when I arrive at the Clear Data option? Thanks! Dave

If you allow cookies by default, you can still block them for a certain site. On your computer, open Chrome. ... Under "Privacy and security," click Site settings Cookies. Next to "Block," "Clear on exit," or "Allow," select Add.

Apart from @cor-el's answer, you can just use Private Mode (Ctrl+Shift+P) when you are using secret stuff. It's simple life hack, if you need to hide something.

Thanks for your interest Malsha, but all the answers so far are missing my point completely! This is not a general browsing problem. It is a specific maintenance action I wish to perform occasionally when the need arises.

I am very happy that my browser is storing cookies, and I want to keep them intact. I do NOT want to delete any of them when I clear the data cache. I just want to clear out the cache of stored Images and web page code.

Firefox (not Chrome!!) offers a function to clear its cache, but its default settings are to clear BOTH web data and cookies. I just would like to be able to click the clear button without having to UNCHECK the Pre-set ‘Clear Cookies’ button first every time.

So I am looking for the option to change the pre-set default actions of these checkboxes.

Does this make my enquiry clearer?

Dave

You can use Private Mode,

Use  Ctrl+Shift+P
It's simple life thing, if you need to hide something from others...

The "Clear Recent History" dialog (Ctrl+Shift+Delete) I mentioned above has a checkbox for each item and this selection is stored in prefs (about:config), so you can only place a checkmark on Cache and remove the checkmark on all others items like the cookies and the browsing history and other that may have a checkmark by default.