diff --git a/xpcom/ds/nsTimelineService.cpp b/xpcom/ds/nsTimelineService.cpp
index d8adec4e140..31ccf95379e 100644
--- a/xpcom/ds/nsTimelineService.cpp
+++ b/xpcom/ds/nsTimelineService.cpp
@@ -226,6 +226,7 @@ PRStatus TimelineInit(void)
 {
     char *timeStr;
     char *fileName;
+    const char *timelineEnable;
     PRInt32 secs, msecs;
     PRFileDesc *fd;
     PRInt64 tmp1, tmp2;
@@ -234,19 +235,19 @@ PRStatus TimelineInit(void)
     NS_WARN_IF_FALSE(status==0, "TimelineService could not allocate TLS storage.");
 
     timeStr = PR_GetEnv("NS_TIMELINE_INIT_TIME");
-
     // NS_TIMELINE_INIT_TIME only makes sense for the main thread, so if it
     // exists, set it there.  If not, let normal thread management code take
     // care of setting the init time.
-    if (timeStr != NULL && 2 == PR_sscanf(timeStr, "%d.%d", &secs, &msecs)) {
+    if (timeStr && *timeStr && (2 == PR_sscanf(timeStr, "%d.%d", &secs, &msecs))) {
         PRTime &initTime = GetThisThreadData()->initTime;
         LL_MUL(tmp1, (PRInt64)secs, 1000000);
         LL_MUL(tmp2, (PRInt64)msecs, 1000);
         LL_ADD(initTime, tmp1, tmp2);
     }
+
     // Get the log file.
     fileName = PR_GetEnv("NS_TIMELINE_LOG_FILE");
-    if (fileName != NULL
+    if (fileName && *fileName
         && (fd = PR_Open(fileName, PR_WRONLY | PR_CREATE_FILE | PR_TRUNCATE,
                          0666)) != NULL) {
         timelineFD = fd;
@@ -256,7 +257,8 @@ PRStatus TimelineInit(void)
     }
 
     // Runtime disable of timeline
-    if (PR_GetEnv("NS_TIMELINE_ENABLE"))
+    timelineEnable = PR_GetEnv("NS_TIMELINE_ENABLE");
+    if (timelineEnable && *timelineEnable)
         gTimelineDisabled = PR_FALSE;
     return PR_SUCCESS;
 }
diff --git a/xpcom/io/nsAppFileLocationProvider.cpp b/xpcom/io/nsAppFileLocationProvider.cpp
index aa7fe14daa8..e071b84cf0d 100755
--- a/xpcom/io/nsAppFileLocationProvider.cpp
+++ b/xpcom/io/nsAppFileLocationProvider.cpp
@@ -255,7 +255,7 @@ nsAppFileLocationProvider::GetFile(const char *prop, PRBool *persistent, nsIFile
         NS_ERROR("Don't use nsAppFileLocationProvider::GetFile(NS_ENV_PLUGINS_DIR, ...). "
                  "Use nsAppFileLocationProvider::GetFiles(...).");
         const char *pathVar = PR_GetEnv("MOZ_PLUGIN_PATH");
-        if (pathVar)
+        if (pathVar && *pathVar)
             rv = NS_NewNativeLocalFile(nsDependentCString(pathVar), PR_TRUE, getter_AddRefs(localFile));
     }
     else if (nsCRT::strcmp(prop, NS_USER_PLUGINS_DIR) == 0)
diff --git a/xpcom/io/nsDirectoryService.cpp b/xpcom/io/nsDirectoryService.cpp
index a4dbf9c066d..4f6f5c53fbb 100644
--- a/xpcom/io/nsDirectoryService.cpp
+++ b/xpcom/io/nsDirectoryService.cpp
@@ -246,18 +246,18 @@ nsDirectoryService::GetCurrentProcessDirectory(nsILocalFile** aFile)
     // regardless of the environment.  This makes it easier to write apps that
     // embed mozilla without having to worry about setting up the environment 
     //
-    // We do this py putenv()ing the default value into the environment.  Note that
+    // We do this by putenv()ing the default value into the environment.  Note that
     // we only do this if it is not already set.
 #ifdef MOZ_DEFAULT_MOZILLA_FIVE_HOME
-    if (PR_GetEnv("MOZILLA_FIVE_HOME") == nsnull)
+    const char *home = PR_GetEnv("MOZILLA_FIVE_HOME");
+    if (!home || !*home)
     {
         putenv("MOZILLA_FIVE_HOME=" MOZ_DEFAULT_MOZILLA_FIVE_HOME);
     }
 #endif
 
     char *moz5 = PR_GetEnv("MOZILLA_FIVE_HOME");
-
-    if (moz5)
+    if (moz5 && *moz5)
     {
         if (realpath(moz5, buf)) {
             localFile->InitWithNativePath(nsDependentCString(buf));
@@ -268,7 +268,7 @@ nsDirectoryService::GetCurrentProcessDirectory(nsILocalFile** aFile)
 #if defined(DEBUG)
     static PRBool firstWarning = PR_TRUE;
 
-    if(!moz5 && firstWarning) {
+    if((!moz5 || !*moz5) && firstWarning) {
         // Warn that MOZILLA_FIVE_HOME not set, once.
         printf("Warning: MOZILLA_FIVE_HOME not set.\n");
         firstWarning = PR_FALSE;
diff --git a/xpcom/reflect/xptinfo/src/xptiInterfaceInfoManager.cpp b/xpcom/reflect/xptinfo/src/xptiInterfaceInfoManager.cpp
index f6640a5ba42..a6cf5abdc2c 100644
--- a/xpcom/reflect/xptinfo/src/xptiInterfaceInfoManager.cpp
+++ b/xpcom/reflect/xptinfo/src/xptiInterfaceInfoManager.cpp
@@ -126,7 +126,7 @@ xptiInterfaceInfoManager::xptiInterfaceInfoManager(nsISupportsArray* aSearchPath
         mSearchPath(aSearchPath)
 {
     const char* statsFilename = PR_GetEnv("MOZILLA_XPTI_STATS");
-    if(statsFilename)
+    if(statsFilename && *statsFilename)
     {
         mStatsLogFile = do_CreateInstance(NS_LOCAL_FILE_CONTRACTID);         
         if(mStatsLogFile && 
@@ -142,7 +142,7 @@ xptiInterfaceInfoManager::xptiInterfaceInfoManager(nsISupportsArray* aSearchPath
     }
 
     const char* autoRegFilename = PR_GetEnv("MOZILLA_XPTI_REGLOG");
-    if(autoRegFilename)
+    if(autoRegFilename && *autoRegFilename)
     {
         mAutoRegLogFile = do_CreateInstance(NS_LOCAL_FILE_CONTRACTID);         
         if(mAutoRegLogFile && 
diff --git a/xpcom/threads/nsEnvironment.cpp b/xpcom/threads/nsEnvironment.cpp
index 139b24a6228..f6e348e122e 100644
--- a/xpcom/threads/nsEnvironment.cpp
+++ b/xpcom/threads/nsEnvironment.cpp
@@ -98,8 +98,7 @@ nsEnvironment::Exists(const nsAString& aName, PRBool *aOutValue)
      * An environment variable does not exist when |getenv()| returns NULL.
      */
     const char *value = PR_GetEnv(nativeName.get());
-    
-    *aOutValue = (value)?(PR_TRUE):(PR_FALSE);
+    *aOutValue = value && *value;
 #else
     /* For non-Unix/Linux platforms we have to fall back to a 
      * "portable" definition (which is incorrect for Unix/Linux!!!!)
@@ -108,7 +107,7 @@ nsEnvironment::Exists(const nsAString& aName, PRBool *aOutValue)
      */
     nsAutoString value;
     Get(aName, value);
-    *aOutValue = (value.IsEmpty())?(PR_FALSE):(PR_TRUE);
+    *aOutValue = !value.IsEmpty();
 #endif /* XP_UNIX */
 
     return NS_OK;
@@ -123,7 +122,7 @@ nsEnvironment::Get(const nsAString& aName, nsAString& aOutValue)
 
     nsCAutoString nativeVal;
     const char *value = PR_GetEnv(nativeName.get());
-    if (value) {
+    if (value && *value) {
         rv = NS_CopyNativeToUnicode(nsDependentCString(value), aOutValue);
     } else {
         aOutValue.Truncate();