Firefox can have a more stable extension architecture, it's called the "Add-on SDK", formerly "Jetpack": https://addons.mozilla.org/en-US/developers/ https://ad

Firefox can have a more stable extension architecture, it's called the "Add-on SDK", formerly "Jetpack": https://addons.mozilla.org/en-US/developers/ https://addons.mozilla.org/en-US/developers/ It's very similar to Chrome's restricted extension APIs, which are the reason that Chrome extensions are not tied to a specific version. If you offer a restricted API, you just have to ensure that that API doesn't break between releases. The problem is with existing Firefox extensions, which are able to use any API in the Mozilla platform, and touch every bit of the Firefox UI. They are essentially executed as if they were part of the browser itself. This approach offers near-unlimited power (you can do anything the browser code can do!) but makes compatibility difficult, since any change to any API can potentially break extensions. Thus extensions have to specify a maximum version of Firefox that they are compatible with. This is both good and bad: it's good in that Firefox extensions are much more powerful than Chrome extensions, but it's bad in that the versioning and compatibility issues are a problem. For Firefox 5, all extensions hosted on addons.mozilla.org were run through a compatibility checker, and if they didn't use any APIs that were impacted in the 4.0 -> 5.0 update, they were marked as compatible with Firefox 5 without any action on the author's part. This helped a lot, but unfortunately there are also a lot of extensions out there that are not hosted on addons.mozilla.org (such as Google Toolbar and other toolbars installed by third-party software, as well as corporate addons).