A script that tweaks the Firefox bundle in OS X to always launch with a specified profile.

.bash_login

# Make your life even easier by adding this line to your .bash_login (or equivalent) file.
alias firefox-bin-profile='~/.bash_profile_scripts/firefox-bin-profile.rb'

firefox-bin-profile.rb

#!/usr/bin/ruby

require 'fileutils'

usage = <<-USAGE
firefox-bin-profile.rb (2011-04-19)
Usage: firefox-bin-profile.rb [--profile <profile_name>] [-rdh]  firefox_app
Options:
--profile <name>  Use the given profile, not the detected version.
-d, --default     A shortcut for --profile 'default'
-r, --revert      Remove the custom bin from this firefox_app.
-h, --help        Show this information.

Customize the given firefox_app to always use a specific profile instead of defaulting to the last used profile.

If no --profile is specified, each time Firefox launches the profile will be selected based on the name of the Firefox.app. For example, with the name "Firefox 4.0.app" the "4.0" profile will be used. With "Firefox Aurora.app" the "Aurora" profile will be used. The given firefox_app .app name must begin with "Firefox" for this feature to work.

Inspired by these instructions: http://hints.macworld.com/article.php?story=20091106222902593
USAGE

manual_profile = nil

flag = ARGV.shift
case flag
when '-r', '--revert'
  flag = :revert
when '-d', '--default'
  manual_profile = 'default'
when '--profile'
  manual_profile = ARGV.shift
when /^--?h(elp)?$/
  puts usage
  exit 0
when /^-/
  puts "invalid option #{flag}\n\n"
  puts usage
  exit 1
else
  # If none of the patterns match, no flags are given & this was the firefox_app path.
  ARGV.unshift(flag)
end

if ARGV.last.nil?
  puts "No firefox_app specified!\n\n"
  puts usage
  exit 1
end

ff_path = File.expand_path(ARGV.last.to_s)
bin_path = File.join(ff_path, 'Contents/MacOS/firefox-bin')
real_path = "#{bin_path}-real"

unless File.exists?(ff_path) && File.exists?(bin_path)
  puts "This firefox_app you provided doesn't look like a copy of Firefox: #{ff_path}\n\n"
  puts usage
  exit 1
end

if flag == :revert
  unless File.exists?(real_path) && `file "#{real_path}"` =~ /binary/
    puts "This copy of Firefox hasn't been updated, so doesn't need reverting: #{ff_path}"
    exit 1
  end
  FileUtils.remove_file(bin_path) if File.exists?(bin_path)
  FileUtils.move(real_path, bin_path)
  puts "This copy of Firefox has been reverted to the default behavior: #{ff_path}"
  exit 0
end

unless `file "#{bin_path}"` =~ /binary/ || (File.exists?(real_path) && `file "#{real_path}"` =~ /binary/)
  puts "This copy of Firefox is in an un-manageable state. Something already happened to the firefox-bin: #{ff_path}"
  exit 1
end

begin
  # If the file in bin_path is a binary, then we need to replace it with our script.
  # This happens when running this script on fresh FF isntalls or after a Firefox update.
  if `file "#{bin_path}"` =~ /binary/
    FileUtils.remove_file(real_path) if File.exists?(real_path)
    FileUtils.move(bin_path, real_path)
  end
  
  File.open(bin_path, 'w') do |bin|
    bin.puts <<-RUBY
#!/usr/bin/ruby

ff_path = File.expand_path(__FILE__)
app_name = ff_path.split('/').detect{|d| d =~ /^Firefox(.*)\.app$/}
real_path = "\#{ff_path}-real"
version = #{ manual_profile ? "'#{manual_profile}'" : "$1.to_s.strip.gsub(/\\s/, ' ')" }
version = version.to_s.gsub(/[^a-z0-9.\\-_ ]/i, '')
version = 'default' if version.empty?

system("\\"\#{real_path}\\" -P '\#{version}' &")
sleep 3
`osascript -e 'tell application "\#{app_name}" to activate'`

    RUBY
  end
  FileUtils.chmod(0755, bin_path)
  if manual_profile
    puts "This copy of Firefox will use the '#{manual_profile}' profile when launching: #{ff_path}"
  else
    puts "This copy of Firefox will use a profile based on its name when launching: #{ff_path}"
  end

rescue
  puts "Reverting back to standard Firefox behavior: #{ff_path}"
  FileUtils.move(real_path, bin_path) if File.exists?(real_path) && `file "#{real_path}"` =~ /binary/
  puts $!.message
  puts $!.backtrace
  exit 1
end