SeaMonkey is an open-source internet suite related to K-Meleon and Firefox. It is maintained by the SeaMonkey Project. It includes a browser, email/newsgroup client, HTML editor, IRC chat, and development tools.

SeaMonkey is a continuation of the Mozilla and Netscape internet suites. These included browsers plus a variety of other internet applications. Netscape initially released the Netscape Communicator suite in 1997 and it became the most popular way to access the internet. Netscape's web browser lost significant market share due to Microsoft combining its Windows operating system and Internet Explorer web browser. To create a new internet suite Netscape spun off Mozilla. Mozilla developed the new Mozilla Internet Suite from the ground up, and Netscape based the versions of their official products up to 7. When Mozilla's standalone web browser Firefox eclipsed the more complex internet suites in market share, Mozilla shifted its focus to Firefox and stopped development of the old internet suite. The SeaMonkey Project emerged as a community effort to maintain a complete internet suite using the same code base as Firefox. In 2017, Mozilla released Firefox Quantum. Quantum completely rewrote huge portions of Firefox to be faster, more stable, and more secure. This has significantly slowed the development of SeaMonkey in part because SeaMonkey still relies on Mozilla's older XUL technology.

Some SeaMonkey add-ons are similar to legacy Firefox add-ons and can work in K-Meleon with minor modifications.