Mozilla has a very fast-paced release cycle for Firefox. New releases are published every six to eight weeks and only the latest version is supported for security issues. This doesn't suit all kind of users so, every 10 cycles, they are promoting one of their release to an Extended Support Release (ESR) which will get security updates (and no functional changes) during the next 10 cycles (which covers a bit more than a year).

Debian has both versions packaged. The ESR one, in the package firefox-esr, is used by default since it is the only version suitable for Debian Stable with its long support period (and even there Debian has to upgrade from one ESR release to the next multiple times during a Debian Stable lifecycle). The regular Firefox is available in the firefox package but it is only available to users of Debian Unstable.

Before Debian Stretch, Firefox and Thunderbird were missing. The iceweasel package contained Iceweasel, which was basically Firefox under another name.

The rationale behind this renaming was a result of the usage rules imposed by the Mozilla Foundation on the Firefox™ registered trademark: any software named Firefox had to use the official Firefox logo and icons. However, since these elements are not released under a free license, Debian could not distribute them in its main section. Rather than moving the whole browser to non-free, the package maintainer choose to use a different name.

出于类似的原因， Thunderbird（雷鸟）™ 邮件客户端被重命名为 Icedove （冰鸽）。

Nowadays, the logo and icons are distributed under a free software license and Mozilla recognized that the changes made by the Debian project are respecting their trademark license so Debian is again able to ship Mozilla's applications under their official name.

当网络刚开始大行其道时，Netscape Navigator 是标准的浏览器，但是当Microsoft 将 Internet Explorer 与 Windows 捆绑在一起并与计算机制造商签订合同禁止他们预装 Netscape Navigator 时，Netscape Navigator 就失去了先机。面对这种困境，网景公司决定开放其源代码，并通过自由许可发布，以使其获得重生。这就是 Mozilla 项目的开始。经过许多年的发展，结果更加让人满意：从 Mozilla 项目带出的 HTML 渲染引擎（Gecko）与标准兼容性最好。该引擎由火狐浏览器使用，而该浏览器也是主要的浏览器之一。