This commit includes the following Mozilla changes: - Bug 1144749 - Add keyboard shortcut to open ReaderView. - Bug 1344211 - Reader view shortcut should be shown in 'View' menu. - Bug 1441788 - Expose Reader View shortcut in the address bar button's tooltip. Please note that Windows users will also need https://bugzilla.mozilla.org/show_bug.cgi?id=1438308 (affects localizations) which isn't included here. References: https://bugzilla.mozilla.org/show_bug.cgi?id=1144749 https://hg.mozilla.org/mozilla-central/rev/c2849a432eee https://bugzilla.mozilla.org/show_bug.cgi?id=1344211 https://hg.mozilla.org/mozilla-central/rev/9c177d80ee84 https://bugzilla.mozilla.org/show_bug.cgi?id=1441788 https://hg.mozilla.org/mozilla-central/rev/5ed5cde4cb2c
