Park, Kim and So (2016) found problems with the accessibility of Coursera, edX, and Khan Academy for users with a disability. Particular problems found were with drop-down menus (toggled on mouse is roll-over), dynamic webpage structures (quiz feedback without page reloading), repetitive elements (course description at the top of each page), illogical focus movement (such as back to top of screen not to next item). Many of the problems appear to be with quizzes. Also the mobile versions of the interface were less accessible than the PC based versions. Also user comments appeared to favor down-loadable content (as in more conventional distance education courses).
What the authors did not address is if Learning Management Systems, such as Moodle, which are not designed for MOOCs, have more accessible interfaces.
Park, K., Kim, H. J., & So, H. J. (2016, January). Are Massive Open Online Courses (MOOCs) Really Open to Everyone?: A Study of Accessibility Evaluation from the Perspective of Universal Design for Learning. In Proceedings of HCI Korea (pp. 29-36). Hanbit Media, Inc. Retrieved from http://dx.doi.org/10.17210/hcik.2016.01.29