[jewel]

You can do this with chrome using the --user-data-dir option, which works fantastically well. For my work gmail I have the following shortcut:

chromium-browser --user-data-dir=~/.profiles/work-mail-profile -app=https://mail.google.com

[packetslave]

But why would you want to do that instead of just using the built-in multiple profiles feature? The only thing I've encountered that required a separate browser instance was using non-default command-line flags for testing something with different proxy options.