Check the Applications section of the Firefox preferences. This is where you can determine how Firefox handles certain types of files. Perhaps it was changed to something other than Always ask or Save file.

Hope this helps.

NOTE: The "jpeg" file may not display in the list. You may need to look at "jpg" file instead.

What file extension do these image files get?

Can't you change the file extension when you save the file?

The only format that I can see when attemting to save a photo is 'preview document'

Thanks for your help :)

Does it mean Preview as in the Apple program for viewing PDF files? Is it really saving as a PDF?