Index: gc_lang/fr/build.py
==================================================================
--- gc_lang/fr/build.py
+++ gc_lang/fr/build.py
@@ -25,10 +25,12 @@
     dVars['webextOptionsHTML'] = _createOptionsForWebExtension(dVars)
     helpers.copyAndFileTemplate("_build/webext/"+sLang+"/manifest.json", "_build/webext/"+sLang+"/manifest.json", dVars)
     helpers.copyAndFileTemplate("_build/webext/"+sLang+"/panel/main.html", "_build/webext/"+sLang+"/panel/main.html", dVars)
     with helpers.CD("_build/webext/"+sLang):
         os.system("web-ext build")
+    # Copy Firefox zip extension to _build
+    helpers.moveFolderContent("_build/webext/"+sLang+"/web-ext-artifacts", "_build", "fx-"+sLang+"-", True)
 
 
 def _createOptionsForWebExtension (dVars):
     sHTML = ""
     sLang = dVars['sDefaultUILang']

Index: helpers.py
==================================================================
--- helpers.py
+++ helpers.py
@@ -70,10 +70,24 @@
         if e.errno == errno.ENOTDIR:
             shutil.copy(spSrc, spDst)
         else:
             raise
 
+
+def moveFolderContent (spSrc, spDst, sPrefix="", bLog=False):
+    "move folder content from <spSrc> to <spDst>: if files already exist in <spDst>, they are replaced. (not recursive)"
+    try:
+        for sf in os.listdir(spSrc):
+            spfSrc = os.path.join(spSrc, sf)
+            if os.path.isfile(spfSrc):
+                spfDst = os.path.join(spDst, sPrefix + sf)
+                shutil.move(spfSrc, spfDst)
+                if bLog:
+                    print("file <" + spfSrc + "> moved to <"+spfDst+">")
+    except:
+        raise
+
 
 def fileFile (spf, dVars):
     "return file <spf> as a text filed with variables from <dVars>"
     return Template(open(spf, "r", encoding="utf-8").read()).safe_substitute(dVars)