How to Install SeaMonkey on Ubuntu 26.04, 24.04 and 22.04

SeaMonkey still fills a specific desktop niche on Ubuntu: one application gives you a web browser, mail and newsgroup client, feed reader, HTML Composer, and IRC chat. Ubuntu’s default repositories do not currently ship SeaMonkey, so to install SeaMonkey on Ubuntu 26.04, 24.04, or 22.04, use the UbuntuZilla APT repository instead of a one-time manual download. UbuntuZilla repackages the official SeaMonkey release as a signed .deb package, which keeps updates inside the normal APT workflow.

The APT workflow adds UbuntuZilla, installs SeaMonkey 2.53.23, verifies the command and desktop launcher, and keeps update and removal paths predictable. If you only need the upstream tarball, the official SeaMonkey download page publishes Linux x64 downloads, but the APT repository is easier to maintain on Ubuntu desktops.

Install SeaMonkey on Ubuntu

Start by refreshing Ubuntu’s package index so APT works from current repository metadata:

sudo apt update

These commands use sudo for package and repository changes. If your account is not allowed to use sudo yet, add the user first with the guide to add a user to sudoers on Ubuntu.

This repository method applies to Ubuntu 26.04, 24.04, and 22.04. SeaMonkey is a graphical desktop application, so package installation happens from a terminal, but normal use still requires an active desktop session.

Install SeaMonkey Repository Prerequisites

Install the tools for HTTPS downloads, GnuPG key conversion, and the runtime library SeaMonkey needs on fresh Ubuntu 26.04 systems:

sudo apt install -y curl ca-certificates gnupg libdbus-glib-1-2

The libdbus-glib-1-2 package is important. Current UbuntuZilla SeaMonkey packages install successfully without it, but a fresh Ubuntu 26.04 system can fail at launch with an XPCOMGlueLoad error until that library is present.

Import the UbuntuZilla Signing Key

The UbuntuZilla project signs its APT repository with the Daniel Folkinshteyn UbuntuZilla key. Download the key from Ubuntu’s keyserver and store it in a dedicated APT keyring:

curl -fsSL "https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x2667CA5C" | sudo gpg --dearmor --yes -o /usr/share/keyrings/ubuntuzilla.gpg

The key fingerprint is C772 05F7 194A 3E1A BE2D F9A4 B7B9 C16F 2667 CA5C. The dedicated keyring keeps UbuntuZilla’s signing key scoped to this repository instead of adding it to a global trusted key list.

Add the UbuntuZilla APT Source

Create a DEB822 source file for the UbuntuZilla repository. The printf command writes each line of the source file, while sudo tee saves it to the root-owned APT configuration directory:

printf '%s\n' \
  'Types: deb' \
  'URIs: https://downloads.sourceforge.net/project/ubuntuzilla/mozilla/apt' \
  'Suites: all' \
  'Components: main' \
  'Signed-By: /usr/share/keyrings/ubuntuzilla.gpg' | sudo tee /etc/apt/sources.list.d/ubuntuzilla.sources > /dev/null

Check the saved file before you continue:

cat /etc/apt/sources.list.d/ubuntuzilla.sources

Expected output:

Types: deb
URIs: https://downloads.sourceforge.net/project/ubuntuzilla/mozilla/apt
Suites: all
Components: main
Signed-By: /usr/share/keyrings/ubuntuzilla.gpg

Refresh APT and Confirm SeaMonkey Packages

Refresh APT again so Ubuntu reads the new UbuntuZilla source:

sudo apt update

Relevant output includes the UbuntuZilla InRelease file and package index:

Get:4 https://downloads.sourceforge.net/project/ubuntuzilla/mozilla/apt all InRelease [3,390 B]
Get:6 https://downloads.sourceforge.net/project/ubuntuzilla/mozilla/apt all/main amd64 Packages [1,090 B]

Confirm APT sees the SeaMonkey package from UbuntuZilla:

apt-cache policy seamonkey-mozilla-build

Expected output:

seamonkey-mozilla-build:
  Installed: (none)
  Candidate: 2.53.23-0ubuntu1
  Version table:
     2.53.23-0ubuntu1 500
        500 https://downloads.sourceforge.net/project/ubuntuzilla/mozilla/apt all/main amd64 Packages

Install the SeaMonkey Package

Install SeaMonkey from UbuntuZilla with APT:

sudo apt install -y seamonkey-mozilla-build

On Ubuntu 26.04, APT 3 summarizes the install like this:

Installing:
  seamonkey-mozilla-build

Summary:
  Upgrading: 0, Installing: 1, Removing: 0, Not Upgrading: 0

Ubuntu 24.04 and 22.04 use older APT wording, but the result is the same: APT downloads and installs the seamonkey-mozilla-build package.

Verify SeaMonkey Installation

Check the installed SeaMonkey version:

seamonkey --version

Expected output:

Mozilla SeaMonkey 2.53.23

Confirm the terminal launcher is on your PATH:

command -v seamonkey

Expected output:

/usr/bin/seamonkey

Launch SeaMonkey on Ubuntu

Launch SeaMonkey from the Terminal

Start the main SeaMonkey browser window from a graphical desktop session with:

seamonkey

SeaMonkey also accepts component flags when you want to open a specific part of the suite directly:

seamonkey -mail        # Open Mail & Newsgroups
seamonkey -composer    # Open HTML Composer
seamonkey -chat        # Open ChatZilla IRC

Run these launch commands from your logged-in desktop session because SeaMonkey opens graphical windows.

Launch SeaMonkey from the Applications Menu

The UbuntuZilla desktop entry uses the label Mozilla Build of Seamonkey. On GNOME, open it from the applications grid:

Activities > Show Applications > Mozilla Build of Seamonkey

Understand SeaMonkey Packages on Ubuntu

UbuntuZilla vs Manual SeaMonkey Downloads

SeaMonkey’s own release page provides Linux x64 tarballs, which are useful for manual testing or custom install layouts. This guide does not document AppImage builds because the official SeaMonkey release page links Linux tarballs, while UbuntuZilla provides the signed APT-managed package. For a normal Ubuntu desktop, the UbuntuZilla package is easier because APT handles installation, package queries, upgrades, and removal. The package name is seamonkey-mozilla-build, but the terminal command is simply seamonkey.

UbuntuZilla is a community-maintained repository, not an Ubuntu archive package. The signed repository and keyring setup reduce tampering risk, but you should still keep SeaMonkey updated and install extensions only from sources you trust.

SeaMonkey HTML Editor, Mail, and Add-ons

SeaMonkey Composer is the built-in HTML editor. Open it with seamonkey -composer or from the Window menu after SeaMonkey starts. Mail and Newsgroups use the same profile directory as the browser suite, so back up ~/.mozilla/seamonkey/ before large profile migrations or before testing add-ons that modify mail or browser behavior.

The built-in Add-ons Manager is available from Tools > Add-ons. SeaMonkey is a legacy Mozilla suite, so add-on compatibility is narrower than current Firefox or Thunderbird extension support.

SeaMonkey System Requirements on Ubuntu

The SeaMonkey system requirements list Linux support for 32-bit and 64-bit systems, but UbuntuZilla currently publishes amd64 and i386 packages. The amd64 package path matches most current Ubuntu desktop installations.

Update or Remove SeaMonkey on Ubuntu

Update SeaMonkey from UbuntuZilla

SeaMonkey updates arrive through the UbuntuZilla repository. To refresh package metadata and update only SeaMonkey, run:

sudo apt update
sudo apt install --only-upgrade seamonkey-mozilla-build

Use sudo apt upgrade instead when you want to apply all pending Ubuntu package updates, not only SeaMonkey.

Remove SeaMonkey from Ubuntu

Remove the SeaMonkey package with:

sudo apt remove --purge -y seamonkey-mozilla-build

On Ubuntu 26.04, relevant output includes:

REMOVING:
  seamonkey-mozilla-build*

Preview dependency cleanup before running any broad autoremove command:

sudo apt autoremove --purge --dry-run

Continue only if the preview lists packages you intended to remove. On reused systems, APT may show unrelated old kernels or desktop packages that have nothing to do with SeaMonkey.

sudo apt autoremove --purge

Then remove the UbuntuZilla source and keyring if you no longer use the repository for SeaMonkey, Firefox, Firefox ESR, or Thunderbird:

sudo rm -f /etc/apt/sources.list.d/ubuntuzilla.sources /usr/share/keyrings/ubuntuzilla.gpg
sudo apt update

Verify the repository files are gone:

test ! -e /etc/apt/sources.list.d/ubuntuzilla.sources && test ! -e /usr/share/keyrings/ubuntuzilla.gpg && echo "UbuntuZilla repository removed"

Expected output:

UbuntuZilla repository removed

Profile warning: SeaMonkey stores browser, mail, Composer, and ChatZilla data under ~/.mozilla/seamonkey/. Do not remove this directory unless you intentionally want to delete your local SeaMonkey profile data.

If you do want to delete SeaMonkey’s profile after backing up anything important, run:

rm -rf ~/.mozilla/seamonkey

Do not delete the wider ~/.mozilla/ directory if you also use Firefox, because Firefox profiles usually live under ~/.mozilla/firefox/.

The prerequisite packages curl, ca-certificates, gnupg, and libdbus-glib-1-2 can also support other software. Leave them installed unless you know they were added only for this SeaMonkey setup.

Troubleshoot SeaMonkey on Ubuntu

Fix XPCOMGlueLoad or libdbus-glib Errors

If SeaMonkey prints an XPCOMGlueLoad error that mentions libdbus-glib-1.so.2, install the missing runtime library and check the version again:

XPCOMGlueLoad error for file /opt/seamonkey/libxul.so:
libdbus-glib-1.so.2: cannot open shared object file: No such file or directory
Couldn't load XPCOM.

sudo apt install -y libdbus-glib-1-2
seamonkey --version

Expected output after the library is installed:

Mozilla SeaMonkey 2.53.23

Replace Old apt-key Instructions

Older UbuntuZilla instructions may still show sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 2667CA5C. Current Ubuntu releases no longer need apt-key for this workflow. Use the dedicated keyring command from this guide instead, then keep Signed-By: /usr/share/keyrings/ubuntuzilla.gpg in the DEB822 source file.

Check UbuntuZilla Repository Access

If sudo apt update cannot fetch UbuntuZilla, check the repository metadata endpoint directly:

curl -L -I https://downloads.sourceforge.net/project/ubuntuzilla/mozilla/apt/dists/all/InRelease

A healthy response redirects through SourceForge and ends with HTTP/1.1 200 OK. The -L flag follows the redirect, while -I requests headers only; see the curl command in Linux guide if you want more flag examples. If SourceForge is slow or temporarily unavailable, wait a few minutes and retry before rebuilding the repository file.

Related Ubuntu Guides

SeaMonkey’s all-in-one design is useful when you want one integrated suite. If you prefer separate applications, these Ubuntu guides fit the nearby workflows:

Install Firefox ESR on Ubuntu for a standalone browser with long-term stability
Install Thunderbird on Ubuntu for a dedicated mail and calendar client
Install Flatpak on Ubuntu when an alternative browser or mail client is available through Flathub

Conclusion

SeaMonkey is installed on Ubuntu through UbuntuZilla, with APT handling future package updates and the seamonkey command available in your desktop session. Use Composer for quick HTML edits, Mail and Newsgroups for local messaging workflows, and the related Firefox ESR or Thunderbird guides when a separate dedicated application fits better.