The latest release of FoxTrick is version 0.12.2.1.
For most browsers, you just need to click one the links bellow. If that doesn't work, download the file and drag'n'drop it into the browser. For Google Chrome 21+
you need to drag the crx file onto the extensions tab (wrench->tools->extensions).
The only mobile browser which supports addons so far is Firefox. Hence, FoxTrick won't work on Opera mobile, Safari mobile or Chrome mobile!