Over the years there have been necessary changes to the web platform that caused legacy websites to break.

Below is a list of those changes.

• SSL removed in favor of TLS wiki (June 2015)
• Adobe Flash (SWF) End of Life wiki (December 2020)
• <applet>, <blink>, and many other tags removed html5 (January 2008)
• window.showModalDialog removed operablog (August 2014)
• Passive touch listeners by default googleblog (January 2017)
• Forms with passwords marked Not Secure over HTTP googleblog (January 2017)
• Array.prototype.flatten breaks MooTools bugzilla renamed to Array.prototype.flat (May 2018)
• Full page layout is no longer synchronous googleblog (May 2018)
• HTML Imports (part of Web Components v0) deprecated googleblog (October 2018)
• WebSQL is removed developer.apple.com (September 2019)
• Cookies changed from SameSite=None to SameSite=Lax by default chromestatus tweet (August 2020)
• alert() and confirm() removed from cross-origin iframes chromestatus tweet (July 2021)
• Removing HTTP/2 Server Push from Chrome chromeblog (August 2022)