Can someone please provide *complete* instructions for taking fullpage screenshots using Developer Toolbar?

Question

Two additional notes:
1. I've found and typed in numerous other examples and absolutely NOTHING has worked. I keep getting "too many arguments" and am thisclose to lighting a torch to Firefox (and also for not providing this information - easily findable - by themselves!). :(
2. Therefore, please make whatever you provide:
a. valid for Firefox 28.0 and (few) previous version(s), and
b. literally broken down into single steps (consisting of ONE action each) so that literally ANYone can follow and EXACTLY duplicate what you are doing. If Grandma can't follow your directions to a perfect result, you're not done! ;)
Many thanks from myself and other frustrated users! :D

Answer 1

UNFORTUNATELY, WHAT YOU'VE SUPPLIED IS MORE OF THE EXACT SAME THING THAT I'VE BEEN SEEING ALL AFTERNOON AND EXACTLY NOTHING LIKE I ASKED FOR, WHICH WAS:
1. TYPE IN FIRST ITEM OF TOTAL COMMAND; YOU WILL THEN SEE X
2. TYPE IN SECOND ITEM OF TOTAL COMMAND; YOU WILL THEN SEE X, ETC.
WHY THIS IS IMPORTANT WILL BECOME SELF-EVIDENT IN FURTHER COMMENTS BELOW....
You can invoke the screenshot command by typing the first letters of the command and press the Tab key to accept the proposed suggestion.
THAT RARELY IF EVER WORKS; I MUST TYPE OUT THE ENTIRE WORD.
https://developer.mozilla.org/Tools
https://developer.mozilla.org/Tools/GCLI
I HAVEN'T YET EXAMINED THESE, BUT MY FEELING IS THAT IT WILL BE MORE OF THE SAME.
Type a space and two hyphens (--) to see the options list and use the Tab key to copy the highlighted entry (fullpage) to the command line.
TAB REALLY DOES ABSOLUTELY NOTHING FOR ME IN THIS CONTEXT.
Note that the fullpage command also has its own options, so you can type the two hyphens another time to see those options.
The default file name is "Screen Shot yyyy-mm-dd at HH.MM.SS.png" in the default Download directory.
See also help screenshot
screenshot --fullpage fullpage_screenshot.png
THE LINE ABOVE IS EXACTLY WHAT DOES NOT WORK.
IF I COPY-PASTE IT IN, A SPACE GETS ADDED. HITTING ENTER RESULTS IN IMAGE 1 (ATTACHED), FOLLOWED BY IMAGE 2 (ATTACHED) WITH ENTER AFTER BACKSPACE TO GET RID OF THE SPACE.
IF I ACTUALLY TYPE IT IN, HITTING ENTER RESULTS IN IMAGE 2.
THE "TRUE" OPTION ALWAYS COMES UP WITH ME UNABLE TO SELECT IT AS SHOWN IN IMAGE 3, LEADING AGAIN TO THE OBSERVED FAILURE MESSAGE IN IMAGE 2.
NOW YOU UNDERSTAND WHY I'M FURIOUS BY NOW! :(
screenshot --fullpage --clipboard true
screenshot --clipboard true --delay 5