can you please give us some context of what language or something that might help us
resolve this issue

http://www.google.co.uk/search?q=webdriver.firefox.useExisting

It's a Selenium 1 features, but docs carry it over to 2.  It's not implemented in Webdriver
code

I would definitely like to see this reimplemented in 2.  Is there another way now to
avoid using the --no-remote parameter to Firefox?

Still not a solution, but I did manage to sidestep by "swallowing" away the --no-remote
param before firefox-bin sees it:

Ruby script:
# Custom Firefox path
Selenium::WebDriver::Firefox.path = "./firefox.sh" 

./firefox.sh:
#!/bin/bash
shift # eats out 1st parameter: --no-remote
unset MOZ_NO_REMOTE  # otherwise separate instance starts
cmd="firefox $*"
echo $cmd && exec $cmd