{{Short description|File format standing for Cross-Platform Install}} {{Infobox file format | name = XPInstall (XPI) | screenshot = | caption = | extension = {{mono|.xpi}} | mime = application/x-xpinstall | owner = Mozilla Foundation | genre = | container for = | contained by = | extended from = | extended to = }} '''XPInstall''' (Cross-Platform Install) was a technology used by the Mozilla Application Suite, SeaMonkey, Mozilla Firefox, Mozilla Thunderbird and other XUL-based applications for installing Mozilla extensions that add functionality to the main application.<ref name="File_org2023">{{cite web | author=File.org | date=2023-02-24 | title=XPI File: How to open XPI file (and what it is) | website=file.org | url=https://file.org/extension/xpi | access-date=2024-02-23}}</ref> Support for XPInstall was removed from Firefox in November 2017 with the release of Firefox 57.<ref>{{Cite web |last=Cimpanu |first=Catalin |title=Old Firefox Add-Ons Will Stop Working in Firefox 57, End of 2017 |url=https://www.bleepingcomputer.com/news/software/old-firefox-add-ons-will-stop-working-in-firefox-57-end-of-2017/ |access-date=2025-11-11 |website=BleepingComputer |language=en-us}}</ref>
== Overview == A XPI (pronounced "zippy" and derived from XPInstall) installer module is a ZIP file that contains an install script or a manifest at the root of the file, and a number of data files.<ref name="File_org2023" /> XPI files allowed users to install add-ons, themes, and other extensions to customize their Mozilla applications.<ref>{{Cite web |date=2016-10-04 |title=XPI - Mozilla {{!}} MDN |url=https://developer.mozilla.org/en-US/docs/Mozilla/XPI |access-date=2025-11-11 |website=developer.mozilla.org |language=en-US }}{{Dead link|date=December 2025 |bot=InternetArchiveBot }}</ref>
In early versions of Mozilla (Firefox before 0.7 and Thunderbird before 0.5),<ref>{{Cite web |title=CVE-2011-2375 |url=https://vulmon.com/vulnerabilitydetails?qid=CVE-2011-2375 |access-date=2025-11-11 |website=vulmon.com}}</ref> the package contained a JavaScript install script (install.js) with '''some''' directives for actions to take during an install, including adding files and directories, removing old or obsolete files and directories, executing command line tools, etc.<ref>{{Cite web |title=CERT/CC Vulnerability Note VU#648758 |url=https://www.kb.cert.org/ |access-date=2025-11-11 |website=www.kb.cert.org}}</ref> In later versions of Firefox and Thunderbird, the install script was replaced by a chrome manifest and a resource description framework file (install.rdf).<ref>{{Cite web |date=2016-10-26 |title=Install Manifests - Mozilla {{!}} MDN |url=https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/Install_Manifests |access-date=2025-11-11 |website=developer.mozilla.org |language=en-US }}{{Dead link|date=December 2025 |bot=InternetArchiveBot }}</ref>
== Deprecation == In August 2015, Mozilla announced plans to deprecate add-ons based on XUL, XPCOM, and the Add-on SDK in favor of a new WebExtensions API.<ref>{{Cite web |last=Needham |first=Kev |date=2015-08-21 |title=The Future of Developing Firefox Add-ons |url=https://blog.mozilla.org/addons/2015/08/21/the-future-of-developing-firefox-add-ons |access-date=2025-11-11 |website=Mozilla Add-ons Community Blog |language=en-US}}</ref> Mozilla cited several reasons for the transition:
* '''Security concerns''': Legacy extensions had unrestricted access to Firefox internals, creating security vulnerabilities * '''Performance issues''': XUL/XPCOM extensions interfered with Firefox's transition to a multiprocess architecture (Electrolysis/e10s) * '''Development complexity''': The tight coupling between Firefox and its add-ons caused development delays and crashes * '''Cross-browser compatibility''': WebExtensions, based on Chrome's extension model, enabled developers to create extensions that worked across multiple browsers
=== Impact === The transition to Firefox 57 affected thousands of extensions.<ref>{{Cite web |last=Brinkmann |first=Martin |date=2017-04-27 |title=If Firefox 57 would be released today, 2273 add-ons would be compatible - gHacks Tech News |url=https://www.ghacks.net/2017/04/27/if-firefox-57-would-be-released-today-2274-add-ons-would-be-compatible/ |access-date=2025-11-11 |website=gHacks Technology News |language=en-US}}</ref> Many popular add-ons were rewritten using the WebExtensions API, while others were discontinued because their functionality could not be replicated within the more restrictive WebExtensions framework.<ref>{{Cite web |last=Cimpanu |first=Catalin |title=Old Firefox Add-Ons Will Stop Working in Firefox 57, End of 2017 |url=https://www.bleepingcomputer.com/news/software/old-firefox-add-ons-will-stop-working-in-firefox-57-end-of-2017/ |access-date=2025-11-11 |website=BleepingComputer |language=en-us}}</ref> The change was controversial within the Firefox community,<ref>{{Cite web |title=Mixed Feelings Greet Mozilla's Add-ons Overhaul |url=https://www.infoq.com/news/2015/08/firefox-addons-announcement/ |access-date=2025-11-11 |website=InfoQ |language=en}}</ref> with some users and developers praising improved cross-browser compatibility while others criticized the loss of customization capabilities.<ref>{{Cite news |title=Firefox 57: Good news? It's nippy. Bad news? It'll also trash your add-ons |url=https://www.theregister.com/2017/11/10/open_source_insider_firefox_57/ |archive-url=https://web.archive.org/web/20250809162629/https://www.theregister.com/2017/11/10/open_source_insider_firefox_57/ |archive-date=2025-08-09 |access-date=2025-11-11 |language=en |url-status=live }}</ref> Some users migrated to Firefox forks such as Pale Moon and Waterfox, which continued to support legacy extensions.<ref>{{Cite web |last=Brinkmann |first=Martin |date=2019-10-25 |title=Waterfox development splits into Classic and Current branches - gHacks Tech News |url=https://www.ghacks.net/2019/10/25/waterfox-development-splits-into-classic-and-current-branches/ |access-date=2025-11-11 |website=gHacks Technology News |language=en-US}}</ref>
== Legacy == The '''.xpi file extension''' continues to be used for WebExtensions in Firefox. Modern XPI files contain a <code>manifest.json</code> file instead of <code>install.rdf</code> and use the WebExtensions API rather than XUL/XPCOM. Several applications maintained XPInstall support after Firefox discontinued it:
* '''Pale Moon''': Forked Firefox's codebase to create the Unified XUL Platform (UXP), which continues to support traditional XUL extensions * '''SeaMonkey''': Re-implemented XUL support for newer codebases, though development has slowed * '''Thunderbird''': Gradually transitioned away from XUL-based extensions, removing support in version 78 (2020)
== See also == {{Portal|Free and open-source software}} * Add-on (Mozilla) * XUL * XPCOM * Browser extension * Mozilla Archive Format
== References == {{Reflist}}
== External links == * {{cite web | url=https://www.mozilla.org/projects/xpinstall/ | archive-url=https://web.archive.org/web/20090422015912/http://www.mozilla.org/projects/xpinstall/ | archive-date=2009-04-22 | title=XPInstall |access-date=2021-09-28 }} * {{cite web | url=https://developer.mozilla.org/en/docs/Extension_Packaging | archive-url=https://web.archive.org/web/20080819132008/https://developer.mozilla.org/en/docs/Extension_Packaging | archive-date=2008-08-19 | title=Extension Packaging – MDC |access-date=2021-09-28 }} * {{cite web | url=https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_first_WebExtension | title=Your first extension – Mozilla | MDN | access-date=2021-09-28 | date=2021-02-19 }}
{{Mozilla projects}}
{{DEFAULTSORT:Xpinstall}} Category:Archive formats Category:Firefox add-ons Category:Firefox extensions Category:Installation software Category:Mozilla Category:Package management systems