Bugzilla

Description:
Please provide an explanation of the feature or change. Include a description of the user scenario in which it would be used and how the user would complete the task(s).
Screenshots and visual UI specs are welcome, but please include sufficient accompanying explanation so that blind members of the accessibility team are able to understand the feature/change.

How do we test this?
If there is an implementation to test, please provide instructions for testing it; e.g. setting preferences, other preparation, how to trigger the UI, etc.

**When will this ship?**
Firefox 100, 
Tracking bug/issue:
[Metabug for all captions support](https://bugzilla.mozilla.org/show_bug.cgi?id=1751505)
[WebVTT captions support](https://bugzilla.mozilla.org/show_bug.cgi?id=1748884) - this patch is available in Nightly 99 behind the 
[Responsive styling for WebVTT captions](https://bugzilla.mozilla.org/show_bug.cgi?id=1751231) 
Design documents (e.g. Product Requirements Document, UI spec): https://www.figma.com/file/XfwsImmxmLvISYhMke6xSF/Picture-in-Picture?node-id=1023%3A2104
Engineering lead: mhowell@mozilla.com
Product manager: amininkova@mozilla.com

The accessibility team has developed the Mozilla Accessibility Release Guidelines which outline what is needed to make user interfaces accessible:
https://wiki.mozilla.org/Accessibility/Guidelines
Please describe the accessibility guidelines you considered and what steps you've taken to address them:

Describe any areas of concern to which you want the accessibility team to give special attention:

My apologies, I have requested the accessibility review prematurely. Will submit the request tomorrow after filling out all the necessary information.