Word from Mozilla is that one of the top crashers of Mozilla Firefox 3.6.13 (current version) is the Skype toolbar. This toolbar works with Firefox to detect phone numbers in webpages, turning them into clickable buttons. This extension is bundled with Skype and is clicked to be installed by default whenever someone downloads or updates Skype. Now Mozilla has found that over the past week this toolbar has been responsible for almost 40,000 crashes of Firefox. That's a lot.
Of course it really depends on the version of Skype Toolbar your using, but furthermore this toolbar uses some methods to detect and re-render phone numbers that will make your DOM manipulation 300 times slower - this effects a large percentage of web content today and is therefor making your whole experience totally crappy. What is Mozilla doing about it?
First, blocklisting the extension: all versions of Skype Toolbar have been added to Mozilla Firefox Blocklist. This is what they call a "soft block" where the extension is temporarily disabled while you the user are notified of the potential problem, at which time you're able to either choose to continue working with it or to get rid of it entirely.