Oh, I forgot to mention in my sibling comment - extensions are frequently pinpointed as the cause of (or a contributing factor to) performance problems. Additionally, many of them rely on older features in the Mozilla architecture, which makes it very hard to fix without breaking extensions that people rely on.<p>While there has been and continues to be significant work in this area, the Web Extensions project has been making great progress and provides a much better means to contain and control extensions, while making the development experience better:<p><a href="https:&#x2F;&#x2F;wiki.mozilla.org&#x2F;WebExtensions&#x2F;" rel="nofollow">https:&#x2F;&#x2F;wiki.mozilla.org&#x2F;WebExtensions&#x2F;</a><p>This is already shipping today and many classic Firefox extensions have already switched over.