Usually, when we talk about plugins that crash our browsers, chances are that we are talking about Adobe’s Flash. Today, however, Mozilla announced that it is blocking the Skype Toolbar from its Firefox browser as it “is one of the top crashers of Mozilla Firefox 3.6.13, and was involved in almost 40,000 crashes of Firefox last week.”

The Skype toolbar examines every page you load for phone numbers and then re-renders these as clickable Skype buttons that enable users to initiate Skype calls right from their browser. According to Mozilla, the re-rendering of these phone numbers slows down some browser functions up to 300 times.

Mozilla is working with Skype to correct these issues and plans to lift this ban once the two companies have found a workable solution that does not lead to crashes and doesn’t slow the browser down.

You can find the full list of Mozilla’s banned add-ons here.