Firefox Cached Web Content

Recently ive been making changes to my web site but so far down the road im seeing things not being updated or very slow to on my page even after deleting the image / text etc server side then uploading again to see if that helps.

In the Firefox settings Advanced / Cached web content, i am clicking on clear now sometimes to help improve the issue.
What is supposed to happen with the settings shown in the image supplied or when the limit cache to 200MB is reached,as when i look its always 200MB.
I was under the thought that when 200 is reached it might do its job then return to 0 ?

 

When the cache limit is reached, the older/outdated data is overwritten.

You can 'force' a page to download a fresh copy of the data by holding down Shift whilst clicking the Refresh button.

 

So when 200MB is reached does it then stay at 200 ?
Should i be having to do anything ?

 

It stays at ~200MB (or w/e you've limited it to), with the oldest data getting flushed for newer data as needed. Ordinarily, there's nothing to do manually, set it and forget it.