I handle most of my email through Gmail's web interface either in Firefox or Chrome.
Often I would like to print -> PDf -> mail pdf to a customer. However the Mail PDF option in the print panel opens up a Mail.app compose window.
Instead I would like this to open a compose panel in whatever browser currently has a copy of Gmail running.
At present I can print directly to PDF, then in Gmail compose, attach, comment, send, then delete the PDF.
An alternative not quite as good solution from my perspective would be for Mail to track the contacts from Gmail so that a few characters would auto complete. But that solution also eludes me.
Best Answer
The only way that I know how to accomplish this is to use Mailplane which is a commercial Mac app for using Gmail's web interface.
It has its own "Mail PDF with Mailplane" service which comes as part of the app:
There's no way that I know of to automate the process of attaching a PDF (or any other file) to Gmail through a web browser. You're going to need a Mac app for that. That either means setting up an email client such as Mail.app (which means duplicating contacts, etc) or Mailplane (which will let you use your existing contacts).