--- a/testing/mochitest/runtests.py
+++ b/testing/mochitest/runtests.py
@@ -78,21 +78,23 @@ except ImportError:
 
 here = os.path.abspath(os.path.dirname(__file__))
 
 
 ########################################
 # Option for MOZ (former NSPR) logging #
 ########################################
 
-# Set the desired log modules you want a log be produced by a try run for, or leave blank to disable the feature.
-# This will be passed to MOZ_LOG_MODULES environment variable. Try run will then put a download link for all log files
+# Set the desired log modules you want a log be produced
+# by a try run for, or leave blank to disable the feature.
+# This will be passed to MOZ_LOG environment variable.
+# Try run will then put a download link for all log files
 # on tbpl.mozilla.org.
 
-MOZ_LOG_MODULES = ""
+MOZ_LOG = ""
 
 #####################
 # Test log handling #
 #####################
 
 # output processing
 
 
@@ -1229,21 +1231,21 @@ toolbar#nav-bar {
                 browserEnv["MOZ_GMP_PATH"] = gmp_path
         except EnvironmentError:
             self.log.error('Could not find path to gmp-fake plugin!')
             return None
 
         if options.fatalAssertions:
             browserEnv["XPCOM_DEBUG_BREAK"] = "stack-and-abort"
 
-        # Produce a mozlog, if setup (see MOZ_LOG_MODULES global at the top of
+        # Produce a mozlog, if setup (see MOZ_LOG global at the top of
         # this script).
-        self.mozLogs = MOZ_LOG_MODULES and "MOZ_UPLOAD_DIR" in os.environ
+        self.mozLogs = MOZ_LOG and "MOZ_UPLOAD_DIR" in os.environ
         if self.mozLogs:
-            browserEnv["MOZ_LOG_MODULES"] = MOZ_LOG_MODULES
+            browserEnv["MOZ_LOG"] = MOZ_LOG
 
         if debugger and not options.slowscript:
             browserEnv["JS_DISABLE_SLOW_SCRIPT_SIGNALS"] = "1"
 
         # For e10s, our tests default to suppressing the "unsafe CPOW usage"
         # warnings that can plague test logs.
         if not options.enableCPOWWarnings:
             browserEnv["DISABLE_UNSAFE_CPOW_WARNINGS"] = "1"

--- a/xpcom/base/Logging.cpp
+++ b/xpcom/base/Logging.cpp
@@ -117,19 +117,30 @@ public:
   /**
    * Loads config from env vars if present.
    */
   void Init()
   {
     bool shouldAppend = false;
     bool addTimestamp = false;
     bool isSync = false;
-    const char* modules = PR_GetEnv("MOZ_LOG_MODULES");
+    const char* modules = PR_GetEnv("MOZ_LOG");
+    if (!modules || !modules[0]) {
+      modules = PR_GetEnv("MOZ_LOG_MODULES");
+      if (modules) {
+        NS_WARNING("MOZ_LOG_MODULES is deprecated."
+            "\nPlease use MOZ_LOG instead.");
+      }
+    }
     if (!modules || !modules[0]) {
       modules = PR_GetEnv("NSPR_LOG_MODULES");
+      if (modules) {
+        NS_WARNING("NSPR_LOG_MODULES is deprecated."
+            "\nPlease use MOZ_LOG instead.");
+      }
     }
 
     NSPRLogModulesParser(modules,
         [&shouldAppend, &addTimestamp, &isSync]
             (const char* aName, LogLevel aLevel) mutable {
           if (strcmp(aName, "append") == 0) {
             shouldAppend = true;
           } else if (strcmp(aName, "timestamp") == 0) {