Python script hangs on ubuntu server using selenium firefox driver - python-2.7

Question

I'm trying to take screenshots of some webpages. I opted for selenium and firefox. I'm using xvfb and setting an environment variable for the display.
The script works fine without xvfb on OS X desktop. However on the server the script hangs after webdriver.Firefox() is issued as if the python script is no longer executing. No exception is ever raised and firefox is still active in my process list.
Setup:
sudo Xvfb :10 -ac
export DISPLAY=:10
test.py
from selenium import webdriver
print 'start'
firefox = webdriver.Firefox()
print 'Hello?'
firefox.quit()
print 'done!'
output:
start
cursor winks tauntingly
I Had the same problem with Chrome. Also tried the phantomJs flash fork, this was successful but did not capture flash content.
starting independently firefox gives
(process:3278): GLib-CRITICAL **: g_slice_set_config: assertion 'sys_page_size == 0' f failed
Xlib: extension "RANDR" missing on display ":10".
Error: Access was denied while trying to open files in your profile directory.
ALSA lib confmisc.c:768:(parse_card) cannot find card '0'
ALSA lib conf.c:4248:(_snd_config_evaluate) function snd_func_card_driver returned error: No such file or directory
ALSA lib confmisc.c:392:(snd_func_concat) error evaluating strings
ALSA lib conf.c:4248:(_snd_config_evaluate) function snd_func_concat returned error: No such file or directory
ALSA lib confmisc.c:1251:(snd_func_refer) error evaluating name
ALSA lib conf.c:4248:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:4727:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM default
(firefox:3278): GConf-WARNING **: Client failed to connect to the D-BUS daemon:
//bin/dbus-launch terminated abnormally without any error message
Please help
Thanks!