gmail app incorrectly identifies Firefox as Safari

[Humphrey van Polanen Petel]

I click on the gmail icon in the launcher and a window opens (presumably some instance of Firefox).
The gmail data is correctly displayed.
However, the banner at the top says that it does not support the Safari browser.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: webapp-container 0.23+14.04.20140428-0ubuntu1
ProcVersionSignature: Ubuntu 3.16.0-49.65~14.04.1-generic 3.16.7-ckt15
Uname: Linux 3.16.0-49-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.13
Architecture: amd64
CurrentDesktop: Unity
Date: Mon Sep 21 11:32:44 2015
ExecutablePath: /usr/bin/webapp-container
InstallationDate: Installed on 2015-09-08 (12 days ago)
InstallationMedia: Ubuntu 14.04.2 LTS "Trusty Tahr" - Release amd64 (20150218.1)
ProcEnviron:
 LANGUAGE=en_AU:en
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_AU.UTF-8
 SHELL=/bin/bash
SourcePackage: webbrowser-app
UpgradeStatus: No upgrade log present (probably fresh install)

[Humphrey van Polanen Petel (hpvpp)]

The banner message is
<This version of Safari is no longer supported. Please upgrade to a supported browser. Dismiss>