Hi!, Fhsamyn,

I think this step help you to sovle your problem,

   From the "History menu", select "Clear Recent History".

   If the menu bar is hidden,
press "Alt" to make it visible.

   From the "Time range to clear": 

drop-down menu, select the desired range; to clear your entire cache, select "Everything".

   Next to "Details", click the down arrow
to choose which elements of the history to clear;
to clear your entire cache, select all items.

   Click "Clear Now".

   Exit/quit all browser windows and re-open the browser.

Dinushi Dhananjani said

Hi!, Fhsamyn, I think this step help you to sovle your problem, From the "History menu", select "Clear Recent History". If the menu bar is hidden, press "Alt" to make it visible. From the "Time range to clear": drop-down menu, select the desired range; to clear your entire cache, select "Everything". Next to "Details", click the down arrow to choose which elements of the history to clear; to clear your entire cache, select all items. Click "Clear Now". Exit/quit all browser windows and re-open the browser.

This article will be helpful to, https://support.mozilla.org/en-US/kb/how-clear-firefox-cache

Looking at the notification in the screenshot it looks you are currently in permanent Private Browsing mode (Always use Private Browsing mode; Never Remember History). When you are in PB mode then you won't be able to clear data stored in the profile folder because in PB mode you use in memory storage. You need exit PB mode and to start Firefox normally if you want to cleanup this cache data.

The problem is that the used space is not reported correctly. The cache is empty but FF reports 153Mb used. I cleared the cache manually.

Thank you for providing this info. When using the steps you described the option clear recent history is greyed out because there is nothing there. The problem is that FF still claims 153Mb in the cache where as a matter of fact the cache is empty. The problems is not about clearing the cache but about the reporting in FF about the cache size which is obviously INCORRECT

You did clear the cache manually when Firefox was closed ?

Are you referring to what is reported when you are in PB mode or when you are in normal mode ?

Firefox will likely report the memory cache when you are in private browsing mode. You can check that on the about:cache page.

Thank you for your reply. The URL about:cache page does not exist in FF70.0 I am referring to the attached output from about:cache which INCORRECTLY reports 153Mb (the actual size used by cache2/entries is 206kb)

There are 387 entries listed according to the screenshot.

Do you see these entries if you click the List link?

Did you try to remove the entire cache2 folder in AppData\Local ?