The final build of Firefox 26 isn't yet available to the public, but those interested in Nightlies can tap into one interesting piece of code right now
26 is set to support CSS Image Orientation -- a feature already supported by rival browsers Chrome and Safari, but only when the image is the top-level document, but not in HTML documents. In other words, web developers have had to resort to a number of workarounds in order to ensure that images weren't mistakenly displayed sideways.
The new CSS image-orientation property, supported in Firefox 26, is the answer once applied to a JPEG image. In use, it'll "take its EXIF orientation tag into account when performing layout and rendering." In other words, by adding just a single CSS property, smartphone and camera images will be displayed in their correct orientation.
Hopefully, the inclusion will become commonplace across all browsers in due time. It sure feels like one of those things that should've been sorted long, long ago.