--- a/browser/installer/windows/nsis/stub.nsi
+++ b/browser/installer/windows/nsis/stub.nsi
@@ -693,17 +693,21 @@ Function createIntro
   Pop $2
   ${SetStretchedTransparentImage} $2 $PLUGINSDIR\appname.bmp $0
 
   ${NSD_CreateBitmap} 0 0 100% 100% ""
   Pop $2
   ${NSD_SetStretchedImage} $2 $PLUGINSDIR\bgintro.bmp $1
 
   GetDlgItem $0 $HWNDPARENT 1 ; Install button
-  SendMessage $0 ${WM_SETTEXT} 0 "STR:$(INSTALL_BUTTON)"
+  ${If} ${FileExists} "$INSTDIR\${FileMainEXE}"
+    SendMessage $0 ${WM_SETTEXT} 0 "STR:$(UPGRADE_BUTTON)"
+  ${Else}
+    SendMessage $0 ${WM_SETTEXT} 0 "STR:$(INSTALL_BUTTON)"
+  ${EndIf}
   ${NSD_SetFocus} $0
 
   GetDlgItem $0 $HWNDPARENT 2 ; Cancel button
   SendMessage $0 ${WM_SETTEXT} 0 "STR:$(CANCEL_BUTTON)"
 
   GetDlgItem $0 $HWNDPARENT 3 ; Back button used for Options
   SendMessage $0 ${WM_SETTEXT} 0 "STR:$(OPTIONS_BUTTON)"
 
@@ -944,17 +948,21 @@ Function createOptions
       SetCtlColors $CheckboxInstallMaintSvc ${OPTIONS_TEXT_COLOR_NORMAL} ${OPTIONS_BKGRD_COLOR}
       SendMessage $CheckboxInstallMaintSvc ${WM_SETFONT} $FontNormal 0
       ${NSD_Check} $CheckboxInstallMaintSvc
     ${EndIf}
   ${EndIf}
 !endif
 
   GetDlgItem $0 $HWNDPARENT 1 ; Install button
-  SendMessage $0 ${WM_SETTEXT} 0 "STR:$(INSTALL_BUTTON)"
+  ${If} ${FileExists} "$INSTDIR\${FileMainEXE}"
+    SendMessage $0 ${WM_SETTEXT} 0 "STR:$(UPGRADE_BUTTON)"
+  ${Else}
+    SendMessage $0 ${WM_SETTEXT} 0 "STR:$(INSTALL_BUTTON)"
+  ${EndIf}
   ${NSD_SetFocus} $0
 
   GetDlgItem $0 $HWNDPARENT 2 ; Cancel button
   SendMessage $0 ${WM_SETTEXT} 0 "STR:$(CANCEL_BUTTON)"
 
   GetDlgItem $0 $HWNDPARENT 3 ; Back button used for Options
   EnableWindow $0 0
   ShowWindow $0 ${SW_HIDE}
@@ -964,17 +972,17 @@ Function createOptions
   ${If} "$WasOptionsButtonClicked" != "1"
     ${If} "$CanWriteToInstallDir" == "false"
       MessageBox MB_OK|MB_ICONEXCLAMATION "$(WARN_WRITE_ACCESS)"
     ${ElseIf} "$HasRequiredSpaceAvailable" == "false"
       MessageBox MB_OK|MB_ICONEXCLAMATION "$(WARN_DISK_SPACE)"
     ${EndIf}
   ${EndIf}
 
-  IntOp $OptionsPageShownCount $OptionsPageShownCount + 1
+  StrCpy $OptionsPageShownCount "1"
 
   System::Call "kernel32::GetTickCount()l .s"
   Pop $StartOptionsPhaseTickCount
 
   LockWindow off
   nsDialogs::Show
 FunctionEnd
 
@@ -1676,16 +1684,23 @@ Function UpdateFreeSpaceLabel
 
 FunctionEnd
 
 Function OnChange_DirRequest
   Pop $0
   System::Call 'user32::GetWindowTextW(i $DirRequest, w .r0, i ${NSIS_MAX_STRLEN})'
   StrCpy $INSTDIR "$0"
   Call UpdateFreeSpaceLabel
+
+  GetDlgItem $0 $HWNDPARENT 1 ; Install button
+  ${If} ${FileExists} "$INSTDIR\${FileMainEXE}"
+    SendMessage $0 ${WM_SETTEXT} 0 "STR:$(UPGRADE_BUTTON)"
+  ${Else}
+    SendMessage $0 ${WM_SETTEXT} 0 "STR:$(INSTALL_BUTTON)"
+  ${EndIf}
 FunctionEnd
 
 Function OnClick_ButtonBrowse
   ; The call to GetLongPath returns a long path without a trailing
   ; back-slash. Append a \ to the path to prevent the directory
   ; name from being appended when using the NSIS create new folder.
   ; http://www.nullsoft.com/free/nsis/makensis.htm#InstallDir
   StrCpy $0 "$INSTDIR" "" -1 ; the last character