I'm using the mozilla packages from the mozilla repo regularly.

Currently I have installed:
Hygiea:~ # rpm -qi MozillaFirefox
Name        : MozillaFirefox
Version     : 44.0
Release     : 2.1
Architecture: x86_64
Install Date: Di 26 Jan 2016 08:59:53 CET
Group       : Productivity/Networking/Web/Browsers
Size        : 102358479
License     : MPL-2.0
Signature   : DSA/SHA1, So 24 Jan 2016 23:14:38 CET, Key ID 026b47f3766da614
Source RPM  : MozillaFirefox-44.0-2.1.src.rpm
Build Date  : So 24 Jan 2016 22:50:18 CET
Build Host  : cloud130
Relocations : (not relocatable)
Vendor      : obs://build.opensuse.org/mozilla
URL         : http://www.mozilla.org/
Summary     : Mozilla Firefox Web Browser
Description :
Mozilla Firefox is a standalone web browser, designed for standards
compliance and performance.  Its functionality can be enhanced via a
plethora of extensions.
Distribution: mozilla / openSUSE_Leap_42.1

My repository config:
Hygiea:~ # zypper lr -d | grep mozilla
 7 | mozilla                   | mozilla                                 | Ja  
     | (r ) Ja         | Ja            |   99      | rpm-md |
http://download.opensuse.org/repositories/mozilla/openSUSE_Leap_42.1/  

In mozilla there is an update for Firefox:
Hygiea:~ # zypper info MozillaFirefox
Daten des Repositories laden ...
Installierte Pakete lesen ...


Informationen f�r Paket MozillaFirefox:
---------------------------------------
Repository: mozilla
Name: MozillaFirefox
Version: 44.0.2-2.1
Arch: x86_64
Anbieter: obs://build.opensuse.org/mozilla
Installiert: Ja
Status: veraltet (Version 44.0-2.1 installiert)
Installierte Gr��e: 97,6 MiB
Zusammenfassung: Mozilla Firefox Web Browser
Beschreibung: 
  Mozilla Firefox is a standalone web browser, designed for standards
  compliance and performance.  Its functionality can be enhanced via a
  plethora of extensions.

But still zypper up does not want to install that
Hygiea:~ # zypper lu
Daten des Repositories laden ...
Installierte Pakete lesen ...
Keine Aktualisierungen gefunden.

while
zypper up MozillaFirefox
Daten des Repositories laden ...
Installierte Pakete lesen ...
Paketabh�ngigkeiten aufl�sen ...

Die folgenden 2 Pakete werden aktualisiert:
  MozillaFirefox MozillaFirefox-translations-common

2 Pakete werden aktualisiert.
Overall download size: 49,2 MiB. Already cached: 0 B. Nach der Operation werden
zus�tzlich 815,0 B belegt.

works correctly.