The Skype Toolbar for Firefox is an extension that re-renders phone numbers in webpages as clickable buttons that can be used to dial the number using the Skype desktop application. As such, Skype itself will continue to work on your computer; this change only affects the Firefox toolbar. Because the toolbar is bundled with the Skype installer, a large number of Firefox users who have installed Skype also have the Skype Toolbar.
"The current shipping version of the Skype Toolbar is one of the top crashers of Mozilla Firefox 3.6.13, and was involved in almost 40,000 crashes of Firefox last week," a Mozilla spokesperson said in a statement. "Additionally, depending on the version of the Skype Toolbar you’re using, the methods it uses to detect and re-render phone numbers can make DOM manipulation up to 300 times slower, which drastically affects the page rendering times of a large percentage of web content served today (plain English: to the user, it appears that Firefox is slow loading web pages). We believe that both of these items constitute a major, user-facing issue, and meet our established criteria for blocklisting an add-on."
Mozilla says it has recently established contact with the Skype Toolbar team. The company will work with them to identify the issues that should be corrected and will lift the soft block on future versions that address those issues.
Skype claims that the latest version fixed the issue already. "Based on our initial investigation, we know that downloading the new client will fix for most users any compatibility issues, and we are working with Mozilla to ensure that there are no other compatibility issues," a Skype spokesperson said in a statement. "We are sorry for any inconvenience this has caused our users. Users can download the latest Skype client with the latest included Toolbars OR the latest toolbar installer itself is here."