When trying to install add-ons for Purebrowser, there is a message that these add-ons are available "Only with Firefox — Get Firefox Now!"
Users should be able to quickly add extensions of their choosing.
Affects e.g. extensions tracked at T644.
Related to T247: Enabling compatibility mode confirmed as workaround.
Should perhaps be fixed on the Mozilla end since PureBrowser identifies as Mozilla / Gecko / Firefox before it identifies as PureBrowser.
Related to T299: Please discuss solutions involving change of addons provider at that other issue.