When we first released extension support in Chromium, we left out all support for running extensions in incognito mode. This meant I had to live without handy extensions like Mouse Stroke and PasswordMaker (shameless plug) whenever I opened an incognito window, and that made me sad. When your muscle memory is trained to expect certain features, it's pretty jarring to find them missing. So in the latest stable version of Google Chrome, I added support for running extensions while in incognito.

One of the main reasons we delayed adding incognito support was that Chrome has no way to ensure that extensions obey the incognito rules: in short, that your browsing data is not saved after you close the incognito window. After much debate, we finally decided to let users decide which extensions they were comfortable using in incognito. You should only enable extensions that you trust and that don't save sensitive information. For example, an extension named Save All Your History would probably not be a good idea to run in incognito, since it would defeat the entire purpose of opening an incognito window. (This is not always the case: if the extension is written with incognito support in mind, it could avoid saving sensitive information, but it is up to the extension developer.)

To allow an extension to run while incognito, open the Extensions management page (accessible from the Tool menu -> Extensions). Each extension has an option to "Allow in incognito". Turning this on will let the extension display page and browser actions in incognito windows, and give them access to browser information originating from an incognito tab. It's just as easy to remove this access any time by following the same steps and unchecking the "Allow in incognito" option.

Note to extension developers: Try to be a good citizen by only persisting browsing information collected from non-incognito windows. You can determine this by examining the incognito property on tab and window objects, or checking chrome.extension.inIncognitoTab from within a content script. For more information, see the extension documentation section on Saving data and incognito mode.