This Instructable will show you how to add an extension to Firefox that lets you search for any word on a web site on Instructables. It's fairly simple, but still cool.
Step 1: Install Dictionary Search
They don't specifically mention it, but it seems to be Firefox 3.0 compatible. It's been running just fine for me.
Step 2: Set for Instructables Search
The first box, labeled "Text," is what is displayed on the submenu. "$" is whatever word or words you highlighted before right-clicking. I just used the text that NachoMahma suggested: Search Instructables for "$".
The second box, labeled "URL," tells it where to search. To search Instructables.com for Instructables containing the selected text, enter https://www.instructables.com/tag/?q=$&limit%3Atype%3Aid=on&type%3Aid=on&type%3Auser=on&type%3Acomment=on&type%3Agroup=on&type%3AforumTopic=on&sort=none. To search the whole site for everything, enter https://www.instructables.com/tag/?sort=none&q=$&limit%3Atype%3Aid=on&limit%3Atype%3Acomment=on&limit%3Atype%3Auser=on&limit%3Atype%3Agroup=on&limit%3Atype%3AforumTopic=on&limit%3Atype%3AforumComment=on.
Step 3: Use
Let's say you were on Sporty's looking at an interesting-but-expensive air conditioner. You decide to see if there's a better option on Instructables, so you do an Instructables search, and get a page full of results. Hmmm...That third one looks nice...