Google Chrome	67.0.3372.1 (Official Build) canary (64-bit) (cohort: Clang-64)
Windows 10 Enterprise Version 1607
JAWS 2018.1803.38 64-bit English 
NVDA 2018.1 

Quick tips for working with dialogs: if you've previously allowed or denied a dialog type and want to trigger it again, please just go to the security chip and change the permission for each dialog type to be "Ask (default)"
Also, if you want to have JAWS or NVDA repeat the text of the dialog, use Insert + b

Steps to repro:

# Launch AT 
# Navigate to https://permission.site
# Select a permission that launches without a default button such as the Location permission. 
# Note that the focus lands on the entire dialog. This is appropriate because there is no default button and therefore focus shouldn't belong on a specific button
# Select another permission that has a default visual and keyboard focus on a specific button such as the USB permission.
Expected: after contents of the dialog is read, the name of the button is read since it has focus
Actual: 

With JAWS, just the name of the button is read. You can then get the contents of the open dialog using Insert + b but the dialog should be read upon opening. After pressing Insert + b, the title of the dialog is read twice. The middle portion of this dialog is never read even using Insert + b.

With NVDA, the dialog title bar is read as well as the focused button. However, the middle portion of the dialog is never read even when using Insert + b. It just says "graphic table" instead of the contents of the table. (that small portion of this bug might be an authoring error)