Context Search (adds a context menu dropdown when you right click highlighted text; think plaintext words you search in trouble ticket type stuff) https://addons.mozilla.org/en-US/firefox/addon/context-searc...
Add To Search Bar (adds an option to search-engine-ify any submit text box) https://addons.mozilla.org/en-US/firefox/addon/add-to-search... (might as well mention https://addons.mozilla.org/en-US/firefox/addon/organize-sear...)
Bonus productivity favorite: https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta...
So yeah, you'll pry Firefox away from my cold dead hands.