I have v1.2 on my nexus 4, and the update function doesn't seem to be working. What is the app.update.url I should point my phone to?

Question

I select 'check for updates' and it will not display anything other than 'checking for updates...' below the button. I do not see any internet traffic in the status bar as it does this. Also, I have left it to 'check for updates' all night, to no avail. Any definitive answers would be great. 'https://update.boot2gecko.org/beta/update.xml' doesn't work and neither does 'https://aus3.mozilla.org/update/3/%PRODUCT%/%VERSION%/%BUILD_ID%/%BUILD_TARGET%/%LOCALE%/%CHANNEL%/%OS_VERSION%/%DISTRIBUTION%/%DISTRIBUTION_VERSION%/update.xml'
I have searched extensively to find where the update channels are located and those, and variants like them, proffer no changes in my situation.
I am starting to wonder if it is the program responsible for checking for updates, or if it is the build for nexus-4 that is having the issue.
Another question that would help in my search to resolve this issue is, does anyone know what program is responsible for checking for these updates?
All help is appreciated, and thank you in advance.

Answer 1

I have since changed my build to master, but this time without using mozilla-central as my gecko path. I have had no issues so far with the stability of the master branch, as I did in the past with mozilla-central as the gecko path.
After having done this, and restoring my /data/local and /data/b2g directories, I am now recieving updates. At least, it updated my marketplace after booting for the first time. Also, I am no longer getting the check now stuck at 'checking for updates...'.
So, I am going to call this solved with changing to master, without using my .userconfig. Further, using Michelle's input, I will periodically git pull, repo update, and reconfigure, build, and flash the master branch.
Thank you all for the help.