Happy1.12 said

As an internet-novice I came across the term 'add-ons' - as I had no idea what that stands for, I went to look it up (tried to, anyway).
Long story short: are add-ons only apllicable to Thunderbird  ?
Now I have two questions  :
1) what are add-ons  ?
2) what is Thunderbird  ?
Not only am I an internet-novice; English is not my native language; so, please:  Have mercy   (keep it simple)  !
Thank you in anticipation  !
Greetings,
Happy112.

https://en.wikipedia.org/wiki/Mozilla_Thunderbird

https://en.wikipedia.org/wiki/Add-on_%28Mozilla%29

And now I see that I've just posted a  'reply'  to my question   I was merely trying to edit my question ......
HELP    !!!
Looks like I'm creating a thread here ......
I even manage to mess up asking a simple question;   (so sorry  !) ....

Hi  mr. Ed  !
Thank you for your reply;  that sure was fast   ! I marked your answer as   'problem solved'  -   am I completely wrong in thinking that Thunderbird is pretty much like Facebook and Twitter  ?
If so,   Thunderbird is not my  'cup of tea' ......
Thank you again   .....   have a nice day    !
Greetings from  'Happy112' .

Hey  ! -   now I still don't know what  'add-ons'  are,   and that's why I wound up here in the first place  .....
I also really need to know how to post a question here properly,   without creating a thread or  'answering'  my own questions; 
I even feel more stupid now   and I really am sorry for being a pain in the ... eh ... neck.

..... and than I noticed  'the-edmeister's  link to add-ons and now I  really  hang my head in shame .......

No, those 2 are nothing like Thunderbird.

Please see these 2 Wikipedia pages: https://en.wikipedia.org/wiki/Facebook https://en.wikipedia.org/wiki/Twitter