Firefox 6.0.x is still in BETA. As with all BETA versions, there are bound to be bugs.

Downgrade to the current version which is 4.0.1. You can download it by clicking the Mozilla Firefox link top left of this forum.

You can specify a file extension like .jpg if Firefox is currently using .html while saving images. You can change the file extension (e.g. to .jpg) of already saved images to make them a valid image. You need to add quotes around the name if Windows is hiding the current (.html) file extension.

You can also try if it works if you save images via Tools > Page Info > Media

Just downloaded that older version. Same problem. Wondering now if it's some kind of Yahoo mail problem. If everyone else experiencing this is using yahoo mail it very well may be. Confused by it all.

Click Save Picture Then where it says "firefox document" use the arrow to open that up and choose "all files" instead. Name your pic and add .JPG on the end and click save.