Hi FireFoxieUser, a few questions:

(1) What method do you use the save the images? For example:

• click a Download button for an image
• right-click the image > Save Image As...
• right-click a link to the image (for example, a thumbnail that leads to a larger image) > Save Link As...
• View the image "stand-alone" in a tab, then Ctrl+s

(2) Do you notice the problem everywhere or only on certain sites?

Hello jscher2000 "firefox opens jpg files as html files after recent update"

Yes, I right click a downloaded image on my 'download folder' on hard drive then 'save image' and saves as "HTML' file with no option to save as (image) .JPG

(1) What method do you use the save the images? For example:

   click a Download button for an image
   right-click the image > Save Image As...

Hi FireFoxieUser, I'm not sure what you mean here:

I right click a downloaded image on my 'download folder' on hard drive

I mean how did you save the image in the first place? How did it get into your download folder?

For a file that's already in your download folder, can see you the file extension or file type? This article describes how to set Windows to always show file extensions: https://www.bleepingcomputer.com/tutorials/how-to-show-file-extensions-in-windows/