Make infowindows a proper dialog
"The popup with more map marker information has everything relating to a dialog window, except it is not announced as such. A screen reader user will not know that it opened, and will additionally not know how to navigate it (tabbing). We suggest adding the role=”dialog” to the popup container div so the user knows it is a popup, and then in the div container with the content change it to role=”document” with tabindex=”0” so the user can access all of the content and not just the native elements that receive tab focus."
(email from Siri & Michelle)