Here is a collection of stock firmware for Vodafone Smart Ultra 6. If you find any missing/updated firmware or receive any OTAs, please post it to this thread. Updates are available at ZTE support site.
 
Do not use TWRP to flash stock firmware! You'll find update.zip and installation instructions within each package. Use stock recovery that is compatible with your stock firmware to install (stock recovery images are in TWRP flashable zips). Czech:
ROM: http://download.ztedevice.com/device/global/support/product/538/5869/sd/2016052514113745.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952139 ro.build.display.id=VDF-995NB01-CZ07b ro.build.version.release=5.1.1 ro.build.date=Thu Mar 10 12:13:39 CST 2016 ro.build.zte_prj_name=P839V55_CZ ro.build.sw_internal_version=CZ_MR3_VDF_P839V55V3.0.0B01 OTA (CZ02c -> CZ_MR01d): n/a - mirror thanks to ovecka ro.build.display.id=VDF-995NB01-CZ_MR01d ro.build.version.release=5.0.2 ro.build.date=Fri Aug 21 02:15:32 CST 2015 ro.build.zte_prj_name=P839V55_CZ ro.build.sw_internal_version=CZ_MR1_VDF_P839V55V1.0.0B06 ROM: http://download.ztedevice.com/device/global/support/product/538/5869/sd/2015072409550343.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952135 ro.build.display.id=VDF-995NB01-CZ02c ro.build.version.release=5.0.2 ro.build.date=Mon May 25 22:27:34 CST 2015 ro.build.zte_prj_name=P839V55_CZ ro.build.sw_internal_version=CZ_VDF_P839V55V1.0.0B13 Germany:
ROM: n/a
Recovery: n/a ro.build.display.id=??? Greece:
ROM: http://download.ztedevice.com/device/global/support/product/541/5878/sd/2016041911215705.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952139 ro.build.display.id=VDF-995NB01-GR07b ro.build.version.release=5.1.1 ro.build.date=Thu Mar 10 12:13:39 CST 2016 ro.build.zte_prj_name=P839V55_GR ro.build.sw_internal_version=GR_MR3_VDF_P839V55V3.0.0B01 ROM: n/a - 2015121609404823.zip
Recovery: n/a ro.build.display.id=VDF-995NB01-GR_MR02b ro.build.version.release=5.1.1 ro.build.date=Mon Nov 16 12:43:16 CST 2015 ro.build.zte_prj_name=P839V55_GR ro.build.sw_internal_version=GR_MR2_VDF_P839V55V1.0.0B09 ROM: n/a - 2015072416211471.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952138 ro.build.display.id=VDF-995NB01-GR03c ro.build.version.release=5.0.2 ro.build.date=Fri May 29 16:44:08 CST 2015 ro.build.zte_prj_name=P839V55_GR ro.build.sw_internal_version=GR_VDF_P839V55V1.0.0B13 Italy:
ROM: n/a
Recovery: n/a ro.build.display.id=??? Ireland:
ROM: http://download.ztedevice.com/device/global/support/product/543/5871/sd/2015121609303084.zip
Recovery: n/a
OTA (IE02c -> IE_MR02b): http://dl1.ztems.com/zxmdmp/download.do?doWhat=getUp&filename=firmwarepackages/HK/ZTE/Vodafone Smart ultra 6/123704/update_IE_VDF_P839V55V1.0.0B13_to_V1.0.0B09.up ro.build.display.id=VDF-995NB01-IE_MR02b ro.build.version.release=5.1.1 ro.build.date=Mon Nov 16 12:43:16 CST 2015 ro.build.zte_prj_name=P839V55_IE ro.build.sw_internal_version=IE_MR2_VDF_P839V55V1.0.0B09 ROM: n/a - 2015072411315002.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952140 ro.build.display.id=VDF-995NB01-IE02c ro.build.version.release=5.0.2 ro.build.date=Mon May 25 22:27:34 CST 2015 ro.build.zte_prj_name=P839V55_IE ro.build.sw_internal_version=IE_VDF_P839V55V1.0.0B13 New Zealand:
ROM: n/a
Recovery: n/a ro.build.display.id=??? Portugal:
ROM: http://download.ztedevice.com/device/global/support/product/568/5867/sd/2016060316165552.zip
Recovery: https://www.androidfilehost.com/?fid=385035244224384600 ro.build.display.id=VDF-995NB01-PT07b ro.build.version.release=5.1.1 ro.build.date=2016年 04月 28日 星期四 11:54:22 CST ro.build.zte_prj_name=P839V55_PT ro.build.sw_internal_version=PT_MR3_VDF_P839V55V3.0.0B02 ROM: n/a - 2016040116590430.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952141 ro.build.display.id=VDF-995NB01-PT_MR06b ro.build.version.release=5.1.1 ro.build.date=Tue Feb 16 15:42:58 CST 2016 ro.build.zte_prj_name=P839V55_PT ro.build.sw_internal_version=PT_MR2_VDF_P839V55V2.0.0B03 ROM: n/a - 2016013018272438.zip 2015121517071246.zip
Recovery: n/a
OTA (PT02c -> PT_MR02b): http://dl1.ztems.com/zxmdmp/download.do?doWhat=getUp&filename=firmwarepackages/HK/ZTE/Vodafone Smart ultra 6/123764/update_PT_VDF_P839V55V1.0.0B13_to_V1.0.0B09.up ro.build.display.id=VDF-995NB01-PT_MR02b ro.build.version.release=5.1.1 ro.build.date=Mon Nov 16 12:43:16 CST 2015 ro.build.zte_prj_name=P839V55_PT ro.build.sw_internal_version=PT_MR2_VDF_P839V55V1.0.0B09 ROM: n/a - 2015072315142830.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952142 ro.build.display.id=VDF-995NB01-PT02c ro.build.version.release=5.0.2 ro.build.date=Mon May 25 22:27:34 CST 2015 ro.build.zte_prj_name=P839V55_PT ro.build.sw_internal_version=PT_VDF_P839V55V1.0.0B13 Romania:
ROM: http://download.ztedevice.com/device/global/support/product/569/5870/sd/2016051817064648.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952145 ro.build.display.id=VDF-995NB01-RO07b ro.build.version.release=5.1.1 ro.build.date=Wed Mar 23 11:05:40 CST 2016 ro.build.zte_prj_name=P839V55_RO ro.build.sw_internal_version=RO_MR3_VDF_P839V55V3.0.0B01 ROM: n/a - 2015072410581176.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952143 ro.build.display.id=VDF-995NB01-RO02c ro.build.version.release=5.0.2 ro.build.date=Mon May 25 22:27:34 CST 2015 ro.build.zte_prj_name=P839V55_RO ro.build.sw_internal_version=RO_VDF_P839V55V1.0.0B13 Spain:
ROM: http://download.ztedevice.com/device/global/support/product/550/5856/sd/2016051114543109.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952139 ro.build.display.id=VDF-995NB01-ES07b ro.build.version.release=5.1.1 ro.build.date=Thu Mar 10 12:13:39 CST 2016 ro.build.zte_prj_name=P839V55_ES ro.build.sw_internal_version=ES_MR3_VDF_P839V55V3.0.0B01 ROM: n/a - 2016010516214116.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952136 ro.build.display.id=VDF-995NB01-ES_MR05b ro.build.version.release=5.1.1 ro.build.date=Wed Dec 16 08:55:12 CST 2015 ro.build.zte_prj_name=P839V55_ES ro.build.sw_internal_version=ES_MR2_VDF_P839V55V1.0.0B15 ROM: n/a - 2015121817071757.zip
Recovery: n/a ro.build.display.id=VDF-995NB01-ES_MR02b ro.build.version.release=5.1.1 ro.build.date=Mon Nov 16 12:43:16 CST 2015 ro.build.zte_prj_name=P839V55_ES ro.build.sw_internal_version=ES_MR2_VDF_P839V55V1.0.0B09 ROM: n/a - 2015091700371589.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952148
OTA (ES02c -> ES_MR01d_2): n/a - update_ES_VDF_P839V55V1.0.0B13_to_V1.0.0B07.up ro.build.display.id=VDF-995NB01-ES_MR01d_2 ro.build.version.release=5.0.2 ro.build.date=Tue Sep 8 10:24:38 CST 2015 ro.build.zte_prj_name=P839V55_ES ro.build.sw_internal_version=ES_MR1_VDF_P839V55V1.0.0B07 ROM: n/a - 2015072414065319.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952147 ro.build.display.id=VDF-995NB01-ES02c ro.build.version.release=5.0.2 ro.build.date=Mon May 25 22:27:34 CST 2015 ro.build.zte_prj_name=P839V55_ES ro.build.sw_internal_version=ES_VDF_P839V55V1.0.0B13 Turkey:
ROM: http://download.ztedevice.com/device/global/support/product/552/5825/sd/2016040515020283.zip http://download.ztedevice.com/support/product/552/5825/sd/20160805172512759.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952139 ro.build.display.id=VDF-995NB01-TR07b ro.build.version.release=5.1.1 ro.build.date=Thu Mar 10 12:13:39 CST 2016 ro.build.zte_prj_name=P839V55_TR ro.build.sw_internal_version=TR_MR3_VDF_P839V55V3.0.0B01 ROM: n/a - 2015112413504851.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952144 ro.build.display.id=VDF-995NB01-TR_MR02b ro.build.version.release=5.1.1 ro.build.date=Mon Nov 16 12:43:16 CST 2015 ro.build.zte_prj_name=P839V55_TR ro.build.sw_internal_version=TR_MR2_VDF_P839V55V1.0.0B09 ROM: n/a - 2015071314155337.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952146 ro.build.display.id=VDF-995NB01-TR03c ro.build.version.release=5.0.2 ro.build.date=Tue Jun 9 10:00:07 CST 2015 ro.build.zte_prj_name=P839V55_TR ro.build.sw_internal_version=TR_VDF_P839V55V1.0.0B16 United Kingdom:
OTA (UK07b -> UK09b): http://dl1.ztems.com/zxmdmp/download.do?doWhat=getUp&filename=firmwarepackages/HK/ZTE/Vodafone Smart ultra 6/387681/update_UK_MR3_VDF_P839V55V3.0.0B01_to_V3.0.0B04.up ro.build.display.id=VDF-995NB01-UK09b ro.build.version.release=5.1.1 ro.build.date=2016年 12月 27日 星期二 13:44:39 CST ro.build.zte_prj_name=P839V55_UK ro.build.sw_internal_version=UK_MR3_VDF_P839V55V3.0.0B04
ROM: http://download.ztedevice.com/device/global/support/product/643/5865/sd/2016041213291898.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952139
OTA (UK_MR02b -> UK07b): n/a - mirror thanks to Grah ro.build.display.id=VDF-995NB01-UK07b ro.build.version.release=5.1.1 ro.build.date=Thu Mar 10 12:13:39 CST 2016 ro.build.zte_prj_name=P839V55_UK ro.build.sw_internal_version=UK_MR3_VDF_P839V55V3.0.0B01 ROM: n/a - 2015122517031087.zip
Recovery: n/a
OTA (UK_MR01d -> UK_MR02b): http://dl1.ztems.com/zxmdmp/download.do?doWhat=getUp&filename=firmwarepackages/HK/ZTE/Vodafone Smart ultra 6/123652/update_UK_MR1_VDF_P839V55V1.0.0B06_to_V1.0.0B09.up ro.build.display.id=VDF-995NB01-UK_MR02b ro.build.version.release=5.1.1 ro.build.date=Mon Nov 16 12:43:16 CST 2015 ro.build.zte_prj_name=P839V55_UK ro.build.sw_internal_version=UK_MR2_VDF_P839V55V1.0.0B09 OTA (UK03c -> UK_MR01d): n/a - mirror thanks to elperroderoke
OTA (UK_MR01b -> UK_MR01d): n/a ro.build.display.id=VDF-995NB01-UK_MR01d ro.build.version.release=5.0.2 ro.build.date=Fri Aug 21 02:15:32 CST 2015 ro.build.zte_prj_name=P839V55_UK ro.build.sw_internal_version=UK_MR1_VDF_P839V55V1.0.0B06 OTA (UK03c -> UK_MR01b): n/a - update_UK_VDF_P839V55V1.0.0B13_to_V1.0.0B03.up ro.build.display.id=VDF-995NB01-UK_MR01b ro.build.version.release=5.0.2 ro.build.date=Fri Jul 17 06:15:09 CST 2015 ro.build.zte_prj_name=P839V55_UK ro.build.sw_internal_version=UK_MR1_VDF_P839V55V1.0.0B03 ROM: n/a - 2015072214222958.zip
Recovery: https://www.androidfilehost.com/?fid=24591000424952137 ro.build.display.id=VDF-995NB01-UK03c ro.build.version.release=5.0.2 ro.build.date=Mon May 25 22:27:34 CST 2015 ro.build.zte_prj_name=P839V55_UK ro.build.sw_internal_version=UK_VDF_P839V55V1.0.0B13