Try using Ctrl-Shift-R or Ctrl-F5 to reload the page. This tells Firefox to reload all of the content on the page, ignoring cached copies of assets.

I'm not sure why this is happening in the first place, though I suspect it may have something to do with the fact that the remote copy is being loaded from a web server (which includes a bunch of headers that help browsers know when to grab a new copy of an asset), while the local copy is being loaded directly through the filesystem.

Thank you grantheaslip, this type of reload does show the changed images.

grantheaslip's suggestion doesn't work for me; no change at all. (Thanks anyway.) Any other ideas? Is there another way to "hard" refresh? I don't see anything in the menu.

Also, it seems like this is a very recent problem. I thought in the past that a regular refresh did the job.

It seems to be a WP issue. If you navigate into one of the pages on your website it loads all the new files. Works for me ;-)

I also find that a "hard" refresh fixes simple changes in css, but when it comes to new images on page there is nothing I can do to get the images to show. The source code that firefox shows indicates the new image should be there. It is like image is missing, but no errors are indicated. All other browsers show the new image on refresh. It is ridiculous that I have to spend so much time, problem sloving this. I have had difficulty in the past but refreshes and restarts usually fix it, now 11.01 this problems is resilient.