Rated 3 out of 5 stars
Perhaps I was previously mistaken. Since my post of May 28th I learned that there isn't only cache on disk, but also memory or ram cache, or at least both were mentioned in what I read (someplace online). If there is non-disk cache in memory or ram, then this might be the sort of internal Firefox cache RAMBack is said to clear or free up.
But Firefox uses its own disk cache folders and these can surely be conceptually thought of as internal to Firefox, as well.
For people who don't know all of the technical details about everything that's involved (especially because a lot really is transparent to users) the description for this extension should be made up-front clear or specific about what caches are cleared by the extension.
Previously, I had only been aware of only cache on disk. If I had heard or read of non-disk cache, before, then it was so seldom that it was easily forgotten. And there are many people who are real novices with computers, which I'm not, but still don't know every technical detail about all aspects of computers and software.
Until this is cleared up, I won't use this extension, but will give it a slightly better rating than the last time.