If you logged into your Gmail account on your Chrome browser and saw a pop-up at the top, it might be a good idea to pay attention to it. It is a pop-up that asks you permission to open all email links (eg: firstname.lastname@example.org) in your Gmail account directly.
If you click on the Use Gmail button, then every time your come across an email link, simply click on it will open a Compose window on your Gmail account.
This is very useful for people who use Gmail on Chrome exclusively for managing their email. If So any email link from any application will open up with compose window with your Gmail account in Chrome.
If you want to do the same with your Firefox browser, use this tutorial to use Gmail as default for opening all email links.
If you are using an email client like Live Mail or Mozilla Thunderbird to manage your email, you might not want to allow Gmail to open all links in Chrome. Otherwise this seems like a logical choice for many.
Do drop in your comments.