SeaMonkey Icon


Web browser with IRC chat, HTML editing, and more.


SeaMonkey is a Web browser that shares much of the same base code as the popular Firefox Web browser. It also contains an advanced e-mail and newsgroup client, IRC chat client, and HTML editor.

The SeaMonkey project is a community effort to deliver production-quality releases of code derived from the application formerly known as "Mozilla Application Suite". Whereas the main focus of the Mozilla Foundation is on Mozilla Firefox and Mozilla Thunderbird, our group of dedicated volunteers works to ensure that you can have "everything but the kitchen sink" and have it stable enough for corporate use.


Known Issues

  • The SSL 3.0 encryption protocol is disabled by default due to security concerns. Legacy websites may still rely on it and will not work with the newer TLS 1.x protocols. SSL 3.0 support can be re-enabled in Preferences under Privacy & Security, SSL.
  • Lightning does not work with SeaMonkey when icaljs is enabled, which it is by default. As a workaround, disable icaljs by setting the calendar.icaljs pref to false in about:config.
  • The Remember Passwords add-on breaks password handling. Please disable or uninstall this add-on using the Add-ons Manager.
  • You cannot set up a new Sync account or pair a device anymore. Workaround: Use an older version of SeaMonkey for such tasks for now.
  • Data loss warning: If you use a profile with this or any later version and then try to go back to SeaMonkey 2.0, SeaMonkey will rename your history file to places.sqlite.corrupt and create a new places.sqlite file, effectively resetting your browsing history. This is because the internal format changed and the upgrade process only works in one direction. Additionally, running MailNews with local folders and POP3 mail filters may produce summary files that are not correctly read by previous versions of SeaMonkey. If you decide to go back to a previous version of SeaMonkey, you should delete the .msf files for your local folders and POP3 accounts or repair the folders using the folder properties dialog in order to avoid potential data loss.
  • After creating a news account through clicking a news URL, the MailNews account wizard may be broken (the account type will always be News). To work around the problem, set the mail.server.serverX.valid pref (where X is the internal number of the corresponding news account) to true in about:config, or delete the invalid news account.
  • Web pages may appear differently in the MailNews feed reader than in the browser. Workaround: Add a "noscript {display:none}" rule to your userContent.css (note that the Stylish add-on cannot be used here since it does not integrate with the MailNews feed reader).
  • Select Element by Click doesn't flash the element in DOM Inspector on Windows if hardware acceleration is enabled.
  • The option "When opening a bookmark group" / "Replace existing tabs" under Preferences / Tabbed Browsing does not have an effect anymore.
  • Lightning keyboard shortcuts for accessing the calendar tab from within the MailNews window or from the main menu (Ctrl+Shift+C/D) do not work..
  • If you try to start SeaMonkey using a locked profile, it will crash.
  • Some synaptic touch pads are unable to vertical scroll.
  • Under certain conditions, scrolling and text input may be jerky.
  • Mac OS X and Windows: Citrix Receiver no longer works. As a workaround, mark the plugin as Always Enable in the Add-ons Manager.
  • Windows: Norton/Symantec anti-virus scanners may report that some parts of SeaMonkey (e.g. the file freebl3.dll) are suspicious. If you downloaded SeaMonkey from one of the official download sites, this is a false alarm. You might experience problems with secure websites when this happens. To fix the issue, instruct your anti-virus software to ignore these files (and move them out of quarantine) and/or switch to another anti-virus software and reinstall SeaMonkey.
  • Linux: The cursor may change to "drag-and-drop" mode in the mail window, causing a hang.
  • Mac: When hardware acceleration is off, background colors in the UI (toolbar, status bar, etc.) might not update correctly when you switch focus from/to a window. Users running Macs with certain older hardware (e.g., Intel GMA 950) will experience this even if they haven't turned off hardware acceleration in Preferences (Appearance/Content).


File Size
77.6 MB
Operating Systems
Mac OS X
System Requirements
  • OS X 10.6 or later
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