You can find this specific version in the official SeaMonkey Legacy Releases archive or via the Mozilla Archive (FTP).
This version is based on the same platform as Firefox 52 ESR, which provides relatively stable web compatibility compared to older browser versions. System Requirements for Windows XP seamonkey xp download
While the SeaMonkey Project has moved to newer versions (like 2.53.x), these require newer operating systems. Version remains the definitive "end of the line" for Windows XP users. You can find this specific version in the
Windows XP Service Pack 3 (SP3) is required for the x86 version. Intel Pentium 4 or newer
A CPU supporting the SSE2 instruction set is mandatory (e.g., Intel Pentium 4 or newer, AMD Athlon 64 or newer).