Install Dictionary Addon and Add the words you need it.

Try this

• https://support.mozilla.org/en-US/kb/how-do-i-use-firefox-spell-checker#w_removing-a-word-you-have-accidentally-added

I just typed a long response (rant) which I could not send. I was signed in, but was told that I needed to sign in.

I need a very low level explanation of jargon, etc. A definition or instruction with jargon term after jargon term is not useful. Often it is like an unknown trail through the woods, never anything around the bend or over the hill with no end.

http://pc.net/glossary/
http://www.webopedia.com/
http://www.techterms.com/

See also http://www.google.com/search?q=dictionary+online