Copy SENDMAIL -> Gmail website

I have recently started using gmail via the web interface instead of using Thunderbird and the one thing I would like to change is to get opus to use gmail website instead of Thunderbird when emailing files, usually photos. When I select a bunch of photos I can right click them and select email files which runs the following command “Copy SENDMAIL”. This opens a box asking if I want to reduce the size of the images and then automatically attaches them to an email and then opens a compose email window. The only problem is this is happening in Thunderbird. Is there anyway to select the photos and then attach them to a gmail email and open the compose email within the gmail website?

I’ve managed to change the mailto: command within firefox so that any mailto: links open the gmail website and then opens the compose window so getting this to work in opus is the final obstacle.

I don't think that this work. The only way could be using Macros for Firefox. Maybe one of this extensions:
addons.mozilla.org/en-US/firefox/addon/3863
seleniumhq.org/projects/ide/

In that case i'm going to have to look at changing the default mail client in the system. I know I can download some software that sits in the system tray to handle this but I was hoping some registry tweak or opus command might save me from doing this.