This tip comes from an old podcast from a TWiT FLOSS podcast with Ben Goodger (Lead Engineer on the Firefox project
Anyways find any search bar and right click on it in the context menu there is a add keyword to this search. Select that and it will bookmark the search, I recommend creating a Search folder in your bookmarks page if you're going to use this a lot. For example we'll use the Linux Mint Forums search. If you right click on the text box and add a keyword say "lmf" without the parentheses the next time you go into the address bar you can type "lmf firefox" without parentheses. This will search linux mint forums for firefox. It's a handy tip for when those websites don't have search plugins for firefox. Give it a try and let me know what you think. I had been using Firefox for a few years now and never knew about this tip.