TwitterAltText от daf

Alt-text makes the web better for everyone, providing a window onto the world otherwise denied to people with vision deficiencies, and enriching the experience for people who can see the image but perhaps lack context.

The point of this extension is to surface alt-text for everyone.

The problem is that alt-text information is currently only surfaced when consuming Twitter through a screen-reader. As a sighted person, it's difficult to tell what alt-text an image has (though an image with alt-text is decorated with an [ALT] overlay, one cannot simply view the alt-text) and not always immediately obvious when an image is missing alt-text, for those who would like help in making the web more inclusive.

This extension is a little experimental, but works. YMMV.