Changes

 Accessibility clients require direct access to information about content. In non-e10s this information is queried directly using sync calls into the DOM. These calls generally arrive on the application main or UI thread and expect a response on return. With e10s, the chrome process generally communicates with content through asynchronous interfaces which is incompatible with current accessibility clients. As such the e10s and Accessibility Teams are working on a new approaches for accessibility clients. Currently accessibility support is enabled for Linux. Windows support should be running in Nightly builds by the end of June with release support rolling out this fall. OSX support rollout is currently TBD. === OSX and Linux === * Sync chrome -> content calls for most common apis, with light weight caching to cut down on the heaviest api traffic.* Gradual improvement using chrome side caching of DOM state, working toward a mostly asynchronous interface. === Windows === See the [https://wiki.mozilla.org/Electrolysis/Accessibility/Windows Windows e10s Accessibility] wiki page for support implementation detail.