diff --git a/toolkit/modules/subprocess/subprocess_win.worker.js b/toolkit/modules/subprocess/subprocess_win.worker.js
index 8363986bc259..22c300bb2a6d 100644
--- a/toolkit/modules/subprocess/subprocess_win.worker.js
+++ b/toolkit/modules/subprocess/subprocess_win.worker.js
@@ -235,6 +235,7 @@ class InputPipe extends Pipe {
       this.overlapped.address()
     );
 
+    // TODO bug 1983138: libc.winLastError should be ctypes.winLastError
     if (!ok && (!this.process.handle || libc.winLastError)) {
       this.onError();
     } else {
@@ -332,6 +333,7 @@ class OutputPipe extends Pipe {
       this.overlapped.address()
     );
 
+    // TODO bug 1983138: libc.winLastError should be ctypes.winLastError
     if (!ok && libc.winLastError) {
       this.onError();
     } else {
@@ -758,11 +760,18 @@ io = {
 
   updatePollEvents() {
     let shouldPoll = false;
-    if (this.processes.size) {
+    for (const process of this.processes.values()) {
       // As long as the process is alive, it may notify IOCP.
-      // When the process exits, we'll remove it from io.processes.
-      shouldPoll = true;
-    } else {
+      // When the process exits, process.handle is cleared by its wait(), which
+      // calls updatePollEvents(), but before it is removed from io.processes.
+      // To ensure that we immediately stop polling if it was the last process,
+      // check if process.handle is set.
+      if (process.handle) {
+        shouldPoll = true;
+        break;
+      }
+    }
+    if (!shouldPoll) {
       for (let pipe of this.pipes.values()) {
         if (pipe.hasPendingIO()) {
           shouldPoll = true;
diff --git a/toolkit/modules/subprocess/subprocess_worker_common.js b/toolkit/modules/subprocess/subprocess_worker_common.js
index ba9c5ce7773a..00ed0bcdc460 100644
--- a/toolkit/modules/subprocess/subprocess_worker_common.js
+++ b/toolkit/modules/subprocess/subprocess_worker_common.js
@@ -153,10 +153,17 @@ let requests = {
     });
   },
 
+  // For testing.
+  getIsPolling() {
+    return { data: io.polling };
+  },
+
+  // For testing.
   getOpenFiles() {
     return { data: new Set(io.pipes.keys()) };
   },
 
+  // For testing.
   getProcesses() {
     let data = new Map(
       Array.from(io.processes.values())
@@ -166,6 +173,7 @@ let requests = {
     return { data };
   },
 
+  // For testing.
   waitForNoProcesses() {
     return Promise.all(
       Array.from(io.processes.values(), proc => proc.awaitFinished())
diff --git a/toolkit/modules/subprocess/test/xpcshell/data_test_script.py b/toolkit/modules/subprocess/test/xpcshell/data_test_script.py
index e1f5f5de93c3..ed2a86e7b74a 100644
--- a/toolkit/modules/subprocess/test/xpcshell/data_test_script.py
+++ b/toolkit/modules/subprocess/test/xpcshell/data_test_script.py
@@ -54,6 +54,10 @@ elif cmd == "ignore_sigterm":
             import time
 
             time.sleep(3600)
+elif cmd == "close_pipes_and_wait_for_stdin":
+    os.close(sys.stdout.fileno())
+    os.close(sys.stderr.fileno())
+    sys.stdin.buffer.read(1)
 elif cmd == "print":
     output(sys.argv[2], stream=sys.stdout, print_only=True)
     output(sys.argv[3], stream=sys.stderr, print_only=True)
diff --git a/toolkit/modules/subprocess/test/xpcshell/test_subprocess_polling.js b/toolkit/modules/subprocess/test/xpcshell/test_subprocess_polling.js
new file mode 100644
index 000000000000..81afe9ec956a
--- /dev/null
+++ b/toolkit/modules/subprocess/test/xpcshell/test_subprocess_polling.js
@@ -0,0 +1,62 @@
+"use strict";
+
+const { getSubprocessImplForTest } = ChromeUtils.importESModule(
+  "resource://gre/modules/Subprocess.sys.mjs"
+);
+
+let PYTHON;
+const TEST_SCRIPT = do_get_file("data_test_script.py").path;
+
+add_setup(async () => {
+  PYTHON = await Subprocess.pathSearch(Services.env.get("PYTHON"));
+});
+
+// When the last process exits, we should stop polling.
+// This is a regression test for bug 1982950
+add_task(async function test_polling_only_when_process_is_running() {
+  let worker = getSubprocessImplForTest().Process.getWorker();
+
+  equal(
+    await worker.call("getIsPolling", []),
+    false,
+    "Initially not polling before starting a program"
+  );
+
+  let proc = await Subprocess.call({
+    command: PYTHON,
+    arguments: ["-u", TEST_SCRIPT, "close_pipes_and_wait_for_stdin"],
+  });
+
+  equal(
+    await worker.call("getIsPolling", []),
+    true,
+    "Is polling while process is active"
+  );
+
+  // TODO bug 1983138: Re-enable this check once readString() resolves on error
+  // instead of timing out.
+  // // This verifies that read() returns when stdout is closed prematurely.
+  // equal(
+  //   await proc.stdout.readString(),
+  //   "",
+  //   "Test program should have closed stdout prematurely without stdout"
+  // );
+
+  equal(
+    await worker.call("getIsPolling", []),
+    true,
+    "Is still polling while process is active"
+  );
+
+  info("Closing stdin to trigger exit");
+  await proc.stdin.close();
+
+  let { exitCode } = await proc.wait();
+  equal(exitCode, 0, "Got expected exit code");
+
+  equal(
+    await worker.call("getIsPolling", []),
+    false,
+    "Not polling when last process has exited"
+  );
+});
diff --git a/toolkit/modules/subprocess/test/xpcshell/xpcshell.toml b/toolkit/modules/subprocess/test/xpcshell/xpcshell.toml
index c0f67d9afb2b..1f3821c167e6 100644
--- a/toolkit/modules/subprocess/test/xpcshell/xpcshell.toml
+++ b/toolkit/modules/subprocess/test/xpcshell/xpcshell.toml
@@ -27,3 +27,5 @@ skip-if = [
 ["test_subprocess_getEnvironment.js"]
 
 ["test_subprocess_pathSearch.js"]
+
+["test_subprocess_polling.js"]