Script Add-On actions??

[Cuffy]

I just downloaded a page from How-to-Geek using that lazyload  user script.
The page seems to load faster without lazyload but lazyload is supposed to speed up loading with an image heavy page??
Could someone that writes script give me a short clue as to how it works? Not technical......... does the script change anything in the page itself, add code, remove code, block code??? I'm baffled about what it do and how?
 
TIA 

[4wd]

You might like to provide links to the How-to-Geek page and the script.  

Just so we don't have to go hunting for them.

[Cuffy]

Sorry, I'm assuming too much........
How-to-Geeks uses a system... function... whatever, that loads images as you scroll down the page. The idea being that a page with a dozen large images loads faster?
If you don't scroll to the bottom of the page you don't get the images loaded and if you save the page, the images aren't saved.
Geeks publishes great articles, many in tutorial format, loaded with large images (screenshots) and I usually recognize a keeper from the title. Open the page, punch Save, and I've got the page! Alas, when I open the page later offline, all the pretty pictures are missing. 
So, go back, find the page, scroll to the bottom and then punch SAVE! I fail to see where I've saved any time getting the info that I wanted, they're selling, using  the infamous "lazyload". Others seem to agree with me if the number of attempts to defeat the system are any indication.
The "nolazyload" script add-on works and if my guess is correct, it works by downloading the images immediately, without scrolling to the bottom and viewing each image before it's saved. I'm curious about how an add-on works? Not just lazyload, but any add-on.
On a page I want to keep, I remove everything that doesn't tell me something I want to know.
Now Sir, my question is: did the add-on enter something to the code in the page that will un-addon the add-on if I remove it?