SeaMonkey 2.1 Alpha 1

These release notes describe system requirements, installation instructions, and known issues for SeaMonkey 2.1 Alpha 1. These notes are updated when we receive feedback, so please check back for new information.

Warning! The SeaMonkey version descibed on this page is an outdated testing-only preview of the next generation of our Internet suite. Please test a newer preview version instead of this one.
For daily use, we strongly advise you to download the current stable release instead.

What's New in SeaMonkey 2.1 Alpha 1

SeaMonkey 2.1 Alpha 1 contains the following major changes relative to SeaMonkey 2.0.5:

  • Better performance on startup and shutdown, as well as for JavaScript.
  • Protection from out-of-date plugins has been implemented.
  • HTML5 video can be played in full screen.
  • Resizeable text areas in web forms.
  • A new Troubleshooting Information page (about:support) is available.
  • MailNews return receipts (MDN) now use notification bars.
  • History expiration has been reworked, and form field autocomplete now also expires its value and orders them based on usage.
  • On Linux, desktop notifications (e.g. mail alerts, finished downloads) show up in the native environment through libnotify.
  • The SSL security system has been changed to fix a renegotiation flaw.
  • CSS :visited selectors have been changed to block ways that websites can quickly check a user's browsing history.
  • The WOFF format for downloadable website fonts is now supported.
  • SMIL animation in SVG is supported, and SVG attributes mapped to CSS properties can now be animated using that. For even more dynamic display, CSS transitions are now supported as well.
  • On Mac OS X, plugins supporting Core Animation rendering can now draw faster and more efficiently.
  • New CSS attributes such as gradients, background sizing, and pointer events have been implemented.
  • A new HTML5 parser is used for all HTML documents, and new DOM and HTML5 features including the Drag & Drop API and the File API, which allow for more interactive web pages, are now supported.
  • JS-ctypes support has been improved, allowing in-application JavaScript code to access native system libraries.
  • Support for WebGL and for Direct2D acceleration on Windows has been added (all disabled by default).
  • Mac OS X 10.4 "Tiger" support has been dropped due to newer features needing system interface only available on 10.5 and higher.

The changes page lists an overview of new features and fixes relative to our last stable release, SeaMonkey 2.0.5.


The SeaMonkey project provides official versions of SeaMonkey 2.1 Alpha 1 for Windows, Linux, and Mac OS X in US English and experimental language packs for a small variety of other languages. Community volunteers are also contributing builds for other platforms. You can download SeaMonkey 2.1 Alpha 1 here.

System Requirements, Installation and Uninstallation

Before installing, make sure your computer meets the system requirements. SeaMonkey 2.1 Alpha 1 will offer to migrate your data from SeaMonkey 1.x or Mozilla 1.x at the first start after installation. You can find more details about installation, profile data and uninstallation in our install and uninstall document.
As this is a developer preview, install it in a different location and use a different profile if you want to make sure it doesn't affect your existing SeaMonkey 2.0 installation.

Extensions and Themes

Extensions installed under SeaMonkey 1.x are not migrated to SeaMonkey 2, and may not be compatible for reinstalling in this version due to major changes in our architecture. Please report any issues to the maintainer of the extension. Extensions and Themes for SeaMonkey 2.1 Alpha 1 can be installed from the SeaMonkey Add-Ons website or the "Get Add-Ons" section in the Add-Ons manager.

Known Issues

This list covers some of the known problems with SeaMonkey 2.1 Alpha 1. Please read this before reporting any new bugs.
  • Reordering of newsgroups using drag & drop doesn't work anymore. (Bug 556887)


  • Some anti-virus software keeps detecting our installers as containing a "Trojan" or "Downloader". This is a false positive and is some wrong detection mechanism in the anti-virus software. The code in question is actually from 7-Zip and decompresses the installer so that its contents can run and install SeaMonkey. That technology is widely used and probably can be used to compress bad as well as good software, but the 7-Zip code itself is perfectly safe. Mozilla scans all our files routinely when putting them on the FTP server and we assure you that our installers are as clean as the official Firefox downloads that are scanned by the same mechanisms.
  • Poorly designed or incompatible extensions can cause problems with SeaMonkey, including make it crash, slow down page display, etc. If you encounter strange problems relating to parts of SeaMonkey no longer working, the browser not starting, windows with strange or distorted appearance, degraded performance, etc, you may be suffering from Extension or Theme trouble. Restart SeaMonkey in Safe Mode. On Windows, start using the "Safe Mode" shortcut created in your Start menu or by running seamonkey.exe -safe-mode. On Linux, start with ./seamonkey -safe-mode and on Mac OS X, run:

    cd /Applications/
    ./seamonkey-bin -safe-mode

    When started in Safe Mode all extensions are disabled and the Default theme is used. Disable the Extension/Theme that is causing trouble and then start normally.
  • If you uninstall an extension that is installed with your user profile (i.e. you installed it from a Web page) and then wish to install it for all user profiles using the -install-global-extension command line flag, you must restart SeaMonkey once to cleanse the profile extensions datasource of traces of that extension before installing with the switch. If you do not do this you may end up with a jammed entry in the Extensions list and will be unable to install the extension globally.
  • If you encounter strange problems relating to bookmarks, downloads, window placement, toolbars, history, or other settings, it is recommended that you try creating a new profile and attempting to reproduce the problem before filing bugs. Create a new profile by running SeaMonkey with the -P command line argument, choose the "Manage Profiles" button and then choose "Create Profile...". Migrate your settings files (Bookmarks, Saved Passwords, etc) over one by one, checking each time to see if the problems resurface. If you do find a particular profile data file is causing a problem, file a bug and attach the file.

Frequently Asked Questions

What can I do to help?
We need help from developers and the testing community to provide as much feedback as possible to make SeaMonkey even better. Please read these notes and the bug filing instructions before reporting any bugs to Bugzilla. You can also give us your feedback through this feedback form.
Why haven't you responded to the mail I sent you?
Use the newsgroup. The SeaMonkey team reads it regularly, and your email may have gotten lost.
Where can I get extensions and themes (add-ons)?
Extensions and Themes can be downloaded from SeaMonkey Add-ons.
Who makes SeaMonkey?
Lots of people. See Help->About SeaMonkey, contributors for a list of some of the people who have contributed to Mozilla and SeaMonkey.
Where's the SeaMonkey 2.1 Alpha 1 source code?
A tarball of the SeaMonkey 2.1 Alpha 1 source code is available at the download page. The latest development code can be obtained from the source repository. SeaMonkey-specific source is in the "suite" directory. Please follow the build instructions.

Other Resources and Links

The following resources contain useful information about SeaMonkey 2.1 Alpha 1: