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 2.53.15 contains (among other changes) the following major changes relative to SeaMonkey 2.53.14:

  • Microtasks and promises bug 1193394.
  • Implement queueMicrotask()bug 1480236.
  • Remove old synchronous contentPrefService from the tree bug 886907 and bug 1392929.
  • Remove remaining uses of 'general.useragent.locale' bug 1410736 and bug 1410738.
  • Migrate to intl.locale.requested.locale list from 'general.useragent.locale' bug 1441016.
  • Introduce a pref to store BCP47 locale list bug 1414390, bug 1423532 and bug 1441026.
  • Remove synchronous certificate verification APIs from nsIX509CertDB bug 1453741 and bug 1453778.
  • Taskbar preview's favicon appears blank bug 1475524.
  • Call Imagelibs decodeImageAsyncWindows using a callback bug 1790695.
  • Remove PermissionsService from process Windows sandboxing code bug 1788233, bug 1789782 and bug 1794394.
  • Security info dialog doesn't show cert status anymore bug 1293378.
  • Replace nsIPlatfromCharset in mailnews bug 1381762.
  • Replace use of nsMsgI18NFileSystemCharset() with NS_CopyUnicodeToNative/NS_CopyNativeToUnicode() bug 1506422.
  • Cater for Outlook's/Hotmail's 'Deleted' folder bug 1320191.
  • Make some filter methods scriptable bug 1497513.
  • Fix crash in nsMsgFilterAfterTheFact::ApplyFilter() caused by async reset of 'm_curFolder' bug 537017.
  • Localize messages from nsIMsgFolder.logRuleHitFail() bug 1352731.
  • Add logging of message filter runs and actions bug 697522.
  • Check that we got a non-null header before running a filter on it (and crashing) bug 1563959.
  • With CONDSTORE, eliminate unneeded flag fetches at startup bug 1428097.
  • Fix so custom tags (keywords) are visible to all users bug 583677.
  • Improve handling of tags on shared folders bug 1596371.
  • Allow setting/resetting junk marking by user for yahoo/aol to stick bug 1260059.
  • Don't check subject if spellchecker is not ready bug 1069787.
  • Grammar issues in mailnews_account_settings.xhtml bug 1793291.
  • Remove use of nsIMemory bug 1792578.
  • Replace obsolete GetStringBundleService call in SeaMonkey bug 1794400.
  • SeaMonkey crashes on macOS Ventura 13.0 bug 1797696.
  • Website Navigation Bar has stopped working bug 1803918.
  • SeaMonkey switch to fullscreen does not work on macOS Ventura 13.0 bug 1804537.
  • Continue the switch from Python 2 to Python 3 in the build system.
  • Added support for clang 15 and macOS SDK 11.3.
  • Verified compatibility with Rust 1.65.

SeaMonkey 2.53.15 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 History is invoked, 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.
  • Support for all NPAPI plugins like Flash, 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 2.53.15 uses the same backend as Firefox and contains the relevant Firefox 60.8 security fixes.

SeaMonkey 2.53.15 shares most parts of the mail and news code with Thunderbird. Please read the Thunderbird 60.8.0 release notes for specific security fixes in this release.

Additional important security fixes up to Current Firefox 102.6 and Thunderbird 102.5 ESR plus many 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.