diff --git a/devtools/client/locales/en-US/webconsole.properties b/devtools/client/locales/en-US/webconsole.properties
index d4bc30d67626..a5ac993e454b 100644
--- a/devtools/client/locales/en-US/webconsole.properties
+++ b/devtools/client/locales/en-US/webconsole.properties
@@ -439,3 +439,12 @@ webconsole.editor.toolbar.closeButton.tooltip=Close Editor (%S)
 # displayed when the console is in regular mode.
 # Parameters: %S is the keyboard shortcut.
 webconsole.input.openEditorButton.tooltip=Open Editor (%S)
+
+# LOCALIZATION NOTE (webconsole.warningGroup.messageCount.tooltip): the tooltip text
+# displayed when you hover a warning group badge (i.e. repeated warning messages for a
+# given category, for example Content Blocked messages) in the web console output.
+# This is a semi-colon list of plural forms.
+# See: http://developer.mozilla.org/en/docs/Localization_and_Plurals
+# #1 number of message in the group.
+# example: 3 messages
+webconsole.warningGroup.messageCount.tooltip=#1 message;#1 messages
diff --git a/devtools/client/webconsole/components/Output/message-types/WarningGroup.js b/devtools/client/webconsole/components/Output/message-types/WarningGroup.js
index 149f268038ab..7ff17d24c52b 100644
--- a/devtools/client/webconsole/components/Output/message-types/WarningGroup.js
+++ b/devtools/client/webconsole/components/Output/message-types/WarningGroup.js
@@ -13,6 +13,12 @@ const Message = createFactory(
   require("devtools/client/webconsole/components/Output/Message")
 );
 
+const { PluralForm } = require("devtools/shared/plural-form");
+const { l10n } = require("devtools/client/webconsole/utils/messages");
+const messageCountTooltip = l10n.getStr(
+  "webconsole.warningGroup.messageCount.tooltip"
+);
+
 WarningGroup.displayName = "WarningGroup";
 
 WarningGroup.propTypes = {
@@ -41,7 +47,7 @@ function WarningGroup(props) {
     dom.span(
       {
         className: "warning-group-badge",
-        title: `${badge} messages`,
+        title: PluralForm.get(badge, messageCountTooltip).replace("#1", badge),
       },
       badge
     ),