There are a few problems with the warning popup that was implemented for #40209 (closed) when using a screen reader. They boil down to:
Not being semantic. E.g. using <xul:description> and <xul:label>.
Not moving focus into the popup, even though it requires a response. This means you cannot navigate it with a screen reader in "browse" mode (Edit: you can move into the popup with F6).
Not moving focus into the popup, even though it requires a response. This means you cannot navigate it with a screen reader in "browse" mode.
This crypto warning uses a popup notification. I spoofed the notification here
I think this is a misuse of the popup notification.
The firefox code is written so that the popup notification is noticed, but can be ignored without interruption. For keyboard and screen reader users, this means they will get an alert that reads out the heading but will not move focus so that the user can continue what they are doing. They can optionally jump into the alert box by pressing F6. This is because the firefox alerts are either shown in reaction to what a web page does (permissions popup), or are triggered by some user action but can be ignored (saved password popups).
This crypto alert doesn't really fit because this is in direct response to the user action, and it seems that the intention of the original issue #40209 (closed) was that it shouldn't be ignored. So it seems that a modal dialog would be more suitable. What do you think? Or would that be too annoying?
Yes, something like that. I think as a first step I might just use the current string with the generic prompt framework. The main difference would be there would no read-only input to show the copied text, it would still be shown in brackets. Once that is done we can see whether it is worth creating a new custom dialog for this.