Cheryl --
Welcome to Apple Discussions !!!!!!
Safari works just fine with Comcast. You don't have to worry about that.
I just tried attaching mail using my Comcast page, and it does work.
It's very very confusing though.
My attach files pane came up, automatically opened to Comcast photo center, where I have no photos stored.
The other tab "My Computer" will take you to your own computer set up. It took a while, but I finally found my desktop and did send something to myself as a test.
BUT, I have all my email accounts set up through the my Mac's Mail application. It's free and it comes with Macs. I just entered my email account names,(I have both Comcast & Earthlinnk) passwords, etc. in Mail's preferences, and I can send and receive through that, and never actually have to go to the Comcast page to do anything. You might want to check that out.
If you want more information on Mail
this is the forum for it. I found this very helpful
when I was setting up my Mail accounts.
Here