Here are screenshots of me editing a page in Mozilla from start to finish.

First, I launch Mozilla and browse to the page I want to edit:

Next, I choose "File-->Edit Page" from the menu.

Up pops Mozilla's editing program, called Composer. You can use this roughly like a word processor.

When you've got the page how you like it, you "publish" it back up to the server. This takes some setup the first time you do it, so choose "File-->Publish As..." from the menu. This will let you fill in some information that tells Mozilla how to save stuff back to the server.

Here's the dialog box you get. Make sure to fill out the second field exactly like you see it here (with the "ftp://" in front and the "public_html" on the end). This tells Mozilla, "okay you found the page at a certain web address, and to save it back to the server so that the changed copy appears at that web address, connect to the server via FTP and treat "public_html" as the root directory of the web site. So, "" (web) = "" (to upload files).

Put our login info (the stuff lunarpages sent in the email) into the username and password fields. Then click "Publish." It should all just work. Then close the Composer window and reload the page you justed edited in the browser. It should be changed: