Caused 33k Firefox crashes in a week

The Skype Toolbar add-on is developed by Skype and comes bundled with the company's popular chat program. The add-on appears to be injected into Firefox automatically while the Skype installation and update process. Its primary function is to identify strings of text in Web pages that look like phone numbers and transparently convert them to links that can be used to automatically dial a call with Skype.

The problems that Mozilla uncovered are fairly serious

Some of the problems that Mozilla uncovered are fairly serious. The toolbar to all appearances performs its phone number conversion routine afterwards every single DOM mutation, severely impairing the browser's performance. In some builds, the performance hit is so bad that it makes DOM manipulation 300 times slower. The add-on's misbehavior as well reportedly causes rendering problems in a number of scenarios.

A Skype employee who joined the discussion in the bug tracker before this month offered to bring the issue to the attention of the relevant Skype personnel. In spite of that and similar efforts by Skype employees to get the right people involved, Mozilla had enormous difficulty getting into direct contact with the team at the VoIP (Voice over Internet Protocol) provider that is in fact responsible for the toolbar.