Unable to install extensions in Firefox webapps

[Shadowstreik]

• 'Alt+T' to pull down Tools menu.
• Select 'Add-Ons & Themes'.
• Search for an extension.
• Click 'Add To Firefox.'

It beings the process and the button disappears while it runs. The Button reappears. The extension has not installed. Clicking again results in the same behavior.

[Th3Rom3]

I have observed this, too. But only if the WebApp is created without a Navbar.
Deleting the contents from userChrome.css (and thus reactivating the navbar) reenables extension installation. Re-adding
#nav-bar, #identity-box, #tabbrowser-tabs, #TabsToolbar { visibility: collapse !important; }
into userChrome.css keeps extensions functional (as far as I can tell) but disables the option to install other extensions.

This might be more an issue on the Firefox side but I thought it would be worthwhile to add some context.

Edit: Looks like a duplicate of (or closely related to) #211

[Shadowstreik]

This may be an issue that should be mitigated within the WebApps application.