The new major release of the all-in-one Internet suite is available for download now. Building on the same Mozilla platform as the newest Firefox release, it delivers the latest developments in web technologies such as HTML5, hardware acceleration and improved JavaScript speed.

SeaMonkey is available in 26 languages, for Windows, Mac OS X and Linux.

Most notably, this release features for the first time:

  • The Content Security Policy (CSP) 1.0 parser has been enabled.
  • The Mixed Content Blocker has been enabled, blocking insecure active content loads on HTTPS pages.
  • New mail alert information can be customized now (Preferences/Mail & Newsgroups/Notifications).
  • A confirmation prompt has been introduced to protect against accidental permanent data loss when force-deleting messages using Shift+Del.
  • MailNews Save As Template supports multiple selections now.
  • The size on disk is now shown for newsgroup folders.
  • Added support for scrollbar style in Mac OS X 10.7 and newer.
  • Enabled mixed content blocking to protects users from man-in-the-middle attacks and eavesdroppers on HTTPS pages.
  • Improved about:memory's functional UI.
  • Enabled DXVA2 on Windows Vista+ to accelerate H.264 video decoding.
  • Simplified interface for notifications of plugin installation.
  • Enabled users to switch the search provider across the entire browser.
  • CSP policies using the standard syntax and semantics will now be enforced.
  • Implemented the HTML5 form control.
  • Added unprefixed requestAnimationFrame.
  • Dropped blink effect from CSS rule text-decoration:blink and completely removed element.
  • Fixed several stability issues.

What's New:

SeaMonkey 2.53.4 contains (among other changes) the following major changes relative to SeaMonkey 2.53.3:

  • Upgraded NSS to 3.53.1 bug 1643859.
  • Updated to Unicode 11 for SpiderMonkey bug 1466471.
  • Updated bundled Twemoji Mozilla font to v0.5.1 to support newer emojis bug 1644346.
  • Updated how photos are handled in the addressbook bug 1641705.
  • Removed outdated RSS feed handlers bug 1643716.
  • Fix initialisation of TodayPane mini-day, to show the right day bug 1479628.
  • Fixed sizing issue of HTML mail question (askSendFormat) dialog bug 1583415.
  • Update of help page content and links.
  • Various security and general platform fixes.
  • SeaMonkey 2.53.4 contains (among other changes) the following major changes relative to SeaMonkey 2.49.5:
  • The Bookmarks Manager has switched its name to Library, and now also includes the History list. When invoking History, the Library will be shown with the History list selected. The extensive modifications were needed because of Mozilla Gecko platform API changes.
  • Download Manager has been migrated to a new API. Although it looks pretty much the same as before, the search option is missing and some other minor details work differently. The previous downloads history is removed during the upgrade.
  • The layout panel was added to the CSS Grid tools.
  • TLS 1.3 is the default SSL version now.
  • The only NPAPI plugin which will work with SeaMonkey 2.53.4 is Flash. Support for other NPAPI plugins like Java and Silverlight has been removed. For displaying pdf files in the browser you can use pdf.js-seamonkey from Isaac Schemm.
  • SeaMonkey now uses a new api for formatting regional data like time and date. Default is to use the application locale of the current SeaMonkey build. If you use a language pack or a different OS formatting this is usually not desired. You can change the formatting from the application locale to the regional settings locale (OS) in the preferences dialog under "Appearance".
  • SeaMonkey 2.53.4 uses the same backend as Firefox and contains the relevant Firefox 60.6 security fixes.
  • SeaMonkey 2.53.4 shares most parts of the mail and news code with Thunderbird. Please read the Thunderbird 60.0 release notes for specific changes and security fixes in this release.
  • Additional important security fixes up to Current Firefox 78.1 ESR and a few enhancements have been backported. We will continue to enhance SeaMonkey security in subsequent 2.53.x beta and release versions as fast as we are able to.