Looks like several people have been facing frequent crashes with Firefox and the Firefox add-ons team is on the case. The Skype Toolbar for Firefox is an extension that detects phone numbers on webpages and allows you to call them using Skype desktop application.
The add-on is bundled with Skype desktop and is automatically installed in Firefox. Mozilla has pinpointed that the current version of Skype toolbar is one of the main culprits behind Firefox crashes. For instance, according to data collected by Mozilla (when users send crash reports to them), the Skype toolbar accounted for 40,000 crashes last week.
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.
Starting today, Mozilla will add the Skype Toolbar to their blacklist and soft block it. With soft blocking they will automatically disable the extension while giving users an option to re-enable it. Mozilla has already blocked several add-ons in the past, some of them include the Bing Bar, Apple QuickTime Plugin, AVG SafeSearch and more. You can view the entire list of blocked add-ons.
Back in 2009, Mozilla had blocked Microsoft .NET and WPF extensions terming them as unsafe for Firefox. Unlike the Skype block, the Microsoft block was hard block, wherein users were not given an option to turn it on. There are only a few extensions which have been hard blocked since then.
There is no official statement or update on this issue from Skype. We will keep you posted when more information becomes available.