--- a/dom/chrome-webidl/ChromeUtils.webidl
+++ b/dom/chrome-webidl/ChromeUtils.webidl
@@ -549,17 +549,17 @@ dictionary ChildProcInfoDictionary {
   long long pid = 0;
   DOMString filename = "";
   unsigned long long virtualMemorySize = 0;
   long long residentSetSize = 0;
   unsigned long long cpuUser = 0;
   unsigned long long cpuKernel = 0;
   sequence<ThreadInfoDictionary> threads = [];
   // Firefox info
-  unsigned long long ChildID = 0;
+  unsigned long long childID = 0;
   UTF8String origin = "";
   WebIDLProcType type = "web";
 };
 
 dictionary ParentProcInfoDictionary {
   // System info
   long long pid = 0;
   DOMString filename = "";

--- a/widget/tests/browser/browser_test_procinfo.js
+++ b/widget/tests/browser/browser_test_procinfo.js
@@ -39,16 +39,20 @@ add_task(async function test_proc_info()
           Assert.ok(
             parentProc.threads.some(thread => thread.name),
             "At least one of the threads of the parent process is named"
           );
         }
 
         for (var i = 0; i < parentProc.children.length; i++) {
           let childProc = parentProc.children[i];
+
+          // By definition, `childID != 0` for children processes.
+          Assert.ok(childProc.childID > 0);
+
           Assert.notEqual(
             childProc.type,
             "browser",
             "Child proc type should not be browser"
           );
           Assert.notEqual(
             childProc.type,
             "unknown",