In permanent private browsing, the extension system attempts to create contexts for the background pages. Those fail. We should probably shortcut extension startup if we're in permanent mode and the extension does not have permission. The addon state should probably also move to disabled.

str:

• create a new profile
• toggle extensions.allowPrivateBrowsingByDefault
• start firefox, enter preferences
• set "never remember history"
• restart
• install an extension with a background page

expected:

• extension is installed as disabled, or since its installed during permanent private browsing we automatically give permission.

actual:

console errors like:

JavaScript error: resource://gre/modules/ExtensionCommon.jsm, line 458: Error: BaseContext attempted to load when extension is not allowed due to incognito settings.
JavaScript error: moz-extension://25208bd2-c3c8-204c-9772-06bb74b3248f/background.js, line 44: ReferenceError: browser is not defined

@mconca, we'll need to decide on a behavior here (see expected behavior above)

Some behavior we need to think about when dealing with permanent private browsing.

We need the permission in order to enable the addon.
I think we will have to install/disable addons when in permanent private browsing, unless we automatically grant permission in this case.

We need to think about UX here:

• We could hide the permission and make enable/disable also add/remove the permission.
• We could hide enable until the permission is given
• What happens for the user when they install, but it is not enabled. Do we show them any UI?

I'm leaning towards:

New extensions installed during permanent private browsing automatically get the permission.
If an existing profile is changed to permanent private browsing, existing extensions that were not previously

This has been discussed, for now we will enable extensions when the are installed into permanent private browsing.

We will not add the permission when a user (who uses permanent private browsing) upgrades to a version supporting this (target 67).

Since the changes are very similar to bug 1525718, merging them into one.