Those functionalities already exist. Keyboard: example: Use 'Tab' key to move about. Each time you press 'tab' it will place focus on the next tabbed item. when it highlightes the first email, then use the arrow keys to move up and down.

OR Go > Next > Message (hold down 'Alt' key then press G, N, M)

There are many keyboard shortcuts to help move around and select items or options.

• https://support.mozilla.org/en-US/kb/keyboard-shortcuts

What I am referring to is being able to scroll through the email content (text body of the email) using the up/down cursor keys or the mousewheel advancing the scroll by a single line at a time. Not 3 or 5 or whatever lines at a time.

You set the movement of the mouse controls in your mouse settings of the operating system.

I do not find any mouse settings for setting the number of lines to be scrolled nor have I found any keyboard settings regarding scrolling.

One thing; which I believe should have been stated at the beginning of this thread, is that I am using Linux Xubuntu 14.04 LTS (Ubuntu based) OS. I will most likely attempt to ask similar query to Ubuntu about this.

I'm certain that there is or are modifications that I can manually make or add to about:config. It's been awhile since I did make changes. I don't remember where I got the info.

The settings in Thunderbird refer to auto scrolling and smooth scrolling. You need to fix the mouse scrolling. Try this info: http://askubuntu.com/questions/160164/how-do-i-enable-middle-mouse-button-emulation-in-12-04-lts

I wish to say thanks to all that have responded. However, if I remember correctly, there is a that modification to the about:config will produce the results for which I am looking for. So ... bye y'all.