--- a/devtools/client/locales/en-US/memory.properties
+++ b/devtools/client/locales/en-US/memory.properties
@@ -206,17 +206,18 @@ tree-item.nostack=(no stack available)
 # available.
 tree-item.nofilename=(no filename available)
 
 # LOCALIZATION NOTE (tree-item.root): The label describing the row in the heap tree
 # that represents the root of the tree when inverted.
 tree-item.root=(root)
 
 # LOCALIZATION NOTE (tree-item.percent): A percent of bytes or count displayed in the tree view.
-tree-item.percent=%S%
+# there are two "%" after %S to escape and display "%"
+tree-item.percent=%S%%
 
 # LOCALIZATION NOTE (diffing.baseline): The name of the baseline snapshot in a
 # diffing comparison.
 diffing.baseline=Baseline
 
 # LOCALIZATION NOTE (diffing.comparison): The name of the snapshot being
 # compared to the baseline in a diffing comparison.
 diffing.comparison=Comparison

--- a/devtools/client/locales/en-US/performance.properties
+++ b/devtools/client/locales/en-US/performance.properties
@@ -100,17 +100,18 @@ table.bytes=%S B
 # LOCALIZATION NOTE (table.ms2):
 # This string is displayed in the call tree after units of time in milliseconds.
 # %S represents the value in milliseconds.
 table.ms2=%S ms
 
 # LOCALIZATION NOTE (table.percentage2):
 # This string is displayed in the call tree after units representing percentages.
 # %S represents the value in percentage with two decimal points, localized.
-table.percentage2=%S%
+# there are two "%" after %S to escape and display "%"
+table.percentage2=%S%%
 
 # LOCALIZATION NOTE (table.root):
 # This string is displayed in the call tree for the root node.
 table.root=(root)
 
 # LOCALIZATION NOTE (table.idle):
 # This string is displayed in the call tree for the idle blocks.
 table.idle=(idle)