Previously, the browser dialogTemplate contained role="dialog" and the Print modal body had no role.
This caused screen readers to extraneously report "dialog, Print grouping".
Dialogs presented with commonDialog.xhtml (e.g. using Services.prompt.alertBC) did have the dialog role on the body, so screen readers would report "dialog, {dialogTitle} dialog".
To fix this, remove role="dialog" from dialogTemplate.
Instead, SubDialog now sets role="dialog" on the dialog document when it loads.
Now, screen readers report just "Print dialog" and "{dialogTitle} dialog", respectively.
Differential Revision: https://phabricator.services.mozilla.com/D87977
4f869a9ad6