Built Firefox, but nothing happens when obj-x86_64-unknown-linux-gnu/dist/bin/firefox is opened

[sachin...@gmail.com]

Hello.
I run Linux 64-bit (Ubuntu 12.04 distro).
I built Firefox for the first time, following the instructions here : https://developer.mozilla.org/en-US/docs/Simple_Firefox_build

I used "./mach build" to start the build process.
I did not configure the build in any way.

The build finished with "995 compiler warnings present".

Following the instructions, I did this to run the Nightly Firefox :
$obj-x86_64-unknown-linux-gnu/dist/bin/firefox

That did nothing. The terminal seemed to have opened a process, so I couldn't use the terminal. But no Firefox window opened.
I had to kill the process myself.

I also tried navigating using the GUI file manager, and double-clicked on "firefox", but that did nothing either.

How do I open the nightly executable?

(oh, and if my stable release firefox is open, doing either of the above, opens
a new window of that with the same profile.)

Thank you.

[Sachin Hosmani]

When I run it in strace, it shows :
futex(0x7fd801d35acc, FUTEX_WAKE_OP_PRIVATE, 1, 1, 0x7fd801d35ac8, {FUTEX_OP_SET, 0, FUTEX_OP_CMP_GT, 1}) = 1

repeatedly on my screen. This doesn't cease. No Firefox window opens, though.

[Sachin Hosmani]

I had never waited earlier and had stopped the process in about 30 seconds.

Now, when I wait, I get a segmentation fault(core dumped) message, in about more than a minute.

I did the whole process again (unbundling mozilla-central.hg, pull, update, build) and when I now open obj-x86_64-unknown-linux-gnu/dist/bin/firefox,

I still get the segmentation fault.

Is any form of diagnosis possible? I don't think I missed any step