commit 98cea4a7ca336b4a509cd1e7bcfe69836a9d1f29
Author: Christoph Moench-Tegeder <cmt@FreeBSD.org>

    Enable WebSerial for FreeBSD
    
    https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=297874
    
    Patch by pcc <pcc@gmx.net>

diff --git dom/webserial/PosixSerialPlatformService.cpp dom/webserial/PosixSerialPlatformService.cpp
index 9389ef0d9821..0786bf5f0dd5 100644
--- dom/webserial/PosixSerialPlatformService.cpp
+++ dom/webserial/PosixSerialPlatformService.cpp
@@ -419,6 +419,32 @@ nsresult PosixSerialPlatformService::EnumeratePortsImpl(
     *aLikelyAccessDenied =
         aPorts.IsEmpty() && (errors == ErrorKind::eAccessDenied);
   }
+#elif defined(XP_FREEBSD)
+  DIR* devDir = opendir("/dev");
+  if (devDir) {
+    auto cleanupDir = MakeScopeExit([&]() { closedir(devDir); });
+    while (struct dirent* ent = readdir(devDir)) {
+      const char* name = ent->d_name;
+      bool isTtyU = strncmp(name, "ttyU", 4) == 0;
+      bool isTtyu = strncmp(name, "ttyu", 4) == 0;
+      if ((!isTtyU && !isTtyu) || name[4] < '0' || name[4] > '9') {
+        continue;
+      }
+      nsAutoCString devpath("/dev/");
+      devpath.Append(name);
+      auto isReal = IsRealSerialPort(devpath.get());
+      if (isReal.isErr()) {
+        continue;
+      }
+      NS_ConvertUTF8toUTF16 path(devpath);
+      IPCSerialPortInfo info;
+      info.id() = path;
+      info.path() = path;
+      info.friendlyName() =
+          NS_ConvertUTF8toUTF16(nsDependentCString(name));
+      aPorts.AppendElement(info);
+    }
+  }
 #endif
 
   MOZ_LOG(gWebSerialLog, LogLevel::Debug,
diff --git dom/webserial/SerialPlatformService.cpp dom/webserial/SerialPlatformService.cpp
index 1da19f340514..a7ce888f6d78 100644
--- dom/webserial/SerialPlatformService.cpp
+++ dom/webserial/SerialPlatformService.cpp
@@ -15,7 +15,8 @@
 namespace mozilla::dom {
 
 #if !defined(XP_WIN) && !defined(XP_MACOSX) && \
-    !(defined(XP_LINUX) && !defined(ANDROID))
+    !(defined(XP_LINUX) && !defined(ANDROID)) && \
+    !defined(XP_FREEBSD)
 already_AddRefed<SerialPlatformService>
 SerialPlatformService::GetInstanceImpl() {
   return MakeAndAddRef<TestSerialPlatformService>();
diff --git dom/webserial/moz.build dom/webserial/moz.build
index bc17c7301d7d..77e4ed2f34ea 100644
--- dom/webserial/moz.build
+++ dom/webserial/moz.build
@@ -25,7 +25,7 @@ if CONFIG["OS_TARGET"] == "WINNT":
         "cfgmgr32",
         "setupapi",
     ]
-elif (CONFIG["OS_TARGET"] == "Darwin" and CONFIG["TARGET_OS"] != "iOS") or CONFIG[
+elif (CONFIG["OS_TARGET"] == "Darwin" and CONFIG["TARGET_OS"] != "iOS") or CONFIG["OS_TARGET"] == "FreeBSD" or CONFIG[
     "OS_TARGET"
 ] == "Linux":
     UNIFIED_SOURCES += [