Internet Explorer 9 (IE9) may be slowed down by Yahoo's new Axis search add-on despite Microsoft and Yahoo being search partners.

After installing the Axis search extension in IE9 on Windows 7, we found that the next time the browser launched, it popped up a message asking if the user wanted to disable Axis and other add-ons to speed up surfing.

The Axis add-on, which displays Yahoo's new search results motif at the bottom of IE, was at the top of the performance-affecting IE extensions installed on the test PC.

According to Microsoft, Yahoo Axis for IE slowed down IE9'S start-up by 0.07 seconds.

The add-on disabling message is not new or somehow triggered by Axis' installation: IE9 has had the feature, officially dubbed "Add-on Performance Advisor" - since the browser launched in March 2011. The Advisor regularly shows warning messages when the combined slow-down time reaches a triggering level.

Yahoo launched Axis earlier this week, offering a free iOS app for the iPhone, iPad and iPod Touch, as well as add-ons for the desktop editions of IE9, Apple's Safari, Google's Chrome and Mozilla's Firefox on Windows, and the latter three on OS X.

The iOS app is essentially Safari with a custom overlay; Apple restricts browsers distributed through the App Store to only those that rely on Safari as its engine.

A security researcher has already reported that the Axis add-on for Chrome contained a private key that could be used by anyone to digitally sign browser extensions in Yahoo's name.

Yahoo acknowledged the key problem and has issued a revised Chrome add-on.

IE9's Add-on Performance Advisor told us that the new Yahoo Axis search extension was slowing down the browser.