diff --git a/browser/installer/windows/nsis/shared.nsh b/browser/installer/windows/nsis/shared.nsh
index ef40317486c9..8fa29eab96ff 100755
--- a/browser/installer/windows/nsis/shared.nsh
+++ b/browser/installer/windows/nsis/shared.nsh
@@ -574,6 +574,7 @@ ${EndIf}
 
   WriteRegStr ${RegKey} "$0\Capabilities\FileAssociations" ".htm"   "FirefoxHTML$2"
   WriteRegStr ${RegKey} "$0\Capabilities\FileAssociations" ".html"  "FirefoxHTML$2"
+  WriteRegStr ${RegKey} "$0\Capabilities\FileAssociations" ".pdf"   "FirefoxHTML$2"
   WriteRegStr ${RegKey} "$0\Capabilities\FileAssociations" ".shtml" "FirefoxHTML$2"
   WriteRegStr ${RegKey} "$0\Capabilities\FileAssociations" ".xht"   "FirefoxHTML$2"
   WriteRegStr ${RegKey} "$0\Capabilities\FileAssociations" ".xhtml" "FirefoxHTML$2"