The QuickWiki extension for Firefox gives you the ability to quickly lookup a word in Wiktionary or Wikipedia without needing to open a new tab up to do so. I have been using this add-on for a while and I do have to say it does make it a little easier to look up words on these two wiki services. If you find yourself quoting either of these sources very often – then this extension is a must download.
Once installed, you can setup specific keyboard shortcuts for both Wiktionary or Wikipedia. For example, you could set it up to use Shift + Right Click to open one and then Ctrl + Right Click to open the other. You also have the option to show QuickWiki on the right click menu or on the status bar.
If you need to search for wiki content in a hurry, I have not run across an add-on that handles this job better. You can pick QuickWiki up at the Firefox Add-ons website.