Thanks Lebell, i was about to post something similiar. To answer the original question, Extensions and Themes are small add-ons for firefox that add additional functionality. How they work all depends on the certain extension. For example the Nuke extension you mentioned ads an option to the right-click menu with the option to nuke various things such as images or selections. The adblock extension ads a small "adblock" tab above all flash content so you can easily click it to disable flash advertisements. The best way to see how certain extensions work is visit their homepage. If you get your extensions from (
https://update.mozilla.org/extension...cation=firefox) each one has a link to the creators home page. Themes are similiar except they all work in the same way, once you install them you must restart firefox. Once restarted click the tools menu, then themes, and select the theme you'd like from the list. I hope this helps and if you have any other questions feel free to ask, and dont worry about the spelling/punctuation, I understood it just fine.