Install the GMail Address Swapper GreaseMonkey Script.
The script would swap the email addresses values between ‘TO” and the “CC” in your GMail compose page. This will work for any compose page (New email or replying to existing conversation).
A new icon (see screen shot below – the new image below the “TO” text) will be auto-inserted when you install the GMail Address Swapper GreaseMonkey Script.
I have just tested that this works on Google Chrome too (Without GreaseMonkey) – Just install the script from UserScripts.org. Let me know if you face any problems in Firefox or Chrome (Doesn’t need GreaseMonkey or GreaseMetal)
Update 2 (Oct 24, 2010)
Chrome 7.0 stable broke this extension. I found a typo in my code which was causing all the icons to appear. I have now fixed it and released the next update for GMail Address Swapper. Let me know if you’re still facing any problems.