v3 is out, get it here.
v2 will be supported for a while, but you'll have to upgrade sooner or later.

The latest stable releases of Chrome, Firefox, Opera and Opera Mobile are supported.

Install 4chan X

Chrome:
  1. Save the 4chan X file from the install button as 4chan_x.user.js.
  2. Drag and drop the file into the extensions page (chrome://chrome/extensions/).
Firefox:
  1. If you don't have Greasemonkey installed:
    1. Install Greasemonkey.
    2. Restart Firefox.
  2. Install 4chan X.
Opera:
  1. If you haven't set your userscripts folder:
    1. Go to Preferences (Ctrl + F12) → Advanced → Content → JavaScript Options → User JavaScript Folder.
    2. Chose what will be your userscripts folder.
    3. Enable User JavaScript on HTTPS and save your settings.
  2. Save the 4chan X file as 4chan_x.js into your userscripts folder.
Opera Mobile:
  1. If you haven't set your userscripts folder:
    1. Open User Prefs.
    2. Enable User JavaScript and User JavaScript on HTTPS.
    3. Set User JavaScript File to what will be your userscripts folder, /sdcard/js for example
    4. Save your settings.
  2. Save the 4chan X file as 4chan_x.js into your userscripts folder.