Index: compile_rules.py
==================================================================
--- compile_rules.py
+++ compile_rules.py
@@ -517,10 +517,11 @@
 
 
 def prepareOptions (lOptionLines):
     "returns a dictionary with data about options"
     sLang = ""
+    sDefaultUILang = ""
     lStructOpt = []
     lOpt = []
     dOptLabel = {}
     dOptPriority = {}
     for sLine in lOptionLines:
@@ -539,18 +540,21 @@
             dOptPriority[m.group(1)] = int(m.group(2))
         elif sLine.startswith("OPTLANG/"):
             m = re.match("OPTLANG/([a-z][a-z](?:_[A-Z][A-Z]|)):(.+)$", sLine)
             sLang = m.group(1)[:2]
             dOptLabel[sLang] = { "__optiontitle__": m.group(2).strip() }
+        elif sLine.startswith("OPTDEFAULTUILANG:"):
+            m = re.match("OPTDEFAULTUILANG: *([a-z][a-z](?:_[A-Z][A-Z]|))$", sLine)
+            sDefaultUILang = m.group(1)[:2]
         elif sLine.startswith("OPTLABEL/"):
             m = re.match("OPTLABEL/([a-z0-9]+):(.+)$", sLine)
             dOptLabel[sLang][m.group(1)] = list(map(str.strip, m.group(2).split("|")))  if "|" in m.group(2)  else  [m.group(2).strip(), ""]
         else:
             print("# Error. Wrong option line in:\n  ")
             print(sLine)
     print("  options defined for: " + ", ".join([ t[0] for t in lOpt ]))
-    dOptions = { "lStructOpt": lStructOpt, "dOptLabel": dOptLabel }
+    dOptions = { "lStructOpt": lStructOpt, "dOptLabel": dOptLabel, "sDefaultUILang": sDefaultUILang }
     dOptions.update({ "dOpt"+k: v  for k, v in lOpt })
     return dOptions, dOptPriority
 
 
 def printBookmark (nLevel, sComment, nLine):
@@ -585,11 +589,11 @@
                 print(sLine.strip())
         elif sLine.startswith("TEST:"):
             lTest.append("{:<8}".format(i) + "  " + sLine[5:].strip())
         elif sLine.startswith("TODO:"):
             pass
-        elif sLine.startswith(("OPTGROUP/", "OPTSOFTWARE:", "OPT/", "OPTLANG/", "OPTLABEL/", "OPTPRIORITY/")):
+        elif sLine.startswith(("OPTGROUP/", "OPTSOFTWARE:", "OPT/", "OPTLANG/", "OPTDEFAULTUILANG:", "OPTLABEL/", "OPTPRIORITY/")):
             lOpt.append(sLine)
         elif re.match("[  \t]*$", sLine):
             pass
         elif sLine.startswith("!!"):
             m = zBookmark.search(sLine)

Index: gc_lang/fr/build.py
==================================================================
--- gc_lang/fr/build.py
+++ gc_lang/fr/build.py
@@ -18,13 +18,27 @@
     "create Web-extension"
     print("Building WebExtension")
     helpers.createCleanFolder("_build/webext/"+sLang)
     dir_util.copy_tree("gc_lang/"+sLang+"/webext/", "_build/webext/"+sLang)
     dir_util.copy_tree("grammalecte-js", "_build/webext/"+sLang+"/grammalecte")
+    dVars['webextOptionsHTML'] = _createOptionsForWebExtension(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")
 
+
+def _createOptionsForWebExtension (dVars):
+    sHTML = ""
+    sLang = dVars['sDefaultUILang']
+    for sSection, lOpt in dVars['lStructOpt']:
+        sHTML += f'\n<div id="subsection_{sSection}" class="opt_subsection">\n  <h2 data-l10n-id="option_{sSection}">{dVars["dOptLabel"][sLang][sSection][0]}</h2>\n'
+        for lLineOpt in lOpt:
+            for sOpt in lLineOpt:
+                sHTML += f'  <p><input type="checkbox" id="option_{sOpt}" /><label id="option_label_{sOpt}" for="option_{sOpt}" data-l10n-id="option_{sOpt}">{dVars["dOptLabel"][sLang][sOpt][0]}</label></p>\n'
+        sHTML += '</div>\n'
+    return sHTML
+
 
 def createFirefoxExtension (sLang, dVars):
     "create extension for Firefox"
     print("Building extension for Firefox")
     helpers.createCleanFolder("_build/xpi/"+sLang)
@@ -52,11 +66,11 @@
                 sHTML += '  <p><input type="checkbox" id="option_'+sOpt+'" /><label id="option_label_'+sOpt+'" for="option_'+sOpt+'" data-l10n-id="option_'+sOpt+'"></label></p>\n'
         sHTML += '</div>\n'
     # Creating translation data
     dProperties = {}
     for sLang in dVars['dOptLabel'].keys():
-        dProperties[sLang] = "\n".join( [ "option_" + sOpt + " = " + dVars['dOptLabel'][sLang][sOpt][0].replace(" [!]", " [!]")  for sOpt in dVars['dOptLabel'][sLang] ] )
+        dProperties[sLang] = "\n".join( [ "option_" + sOpt + " = " + dVars['dOptLabel'][sLang][sOpt][0].replace(" [!]", " [!]")  for sOpt in dVars['dOptLabel'][sLang] ] )
     return sHTML, dProperties
 
 
 def createThunderbirdExtension (sLang, dVars, spLangPack):
     "create extension for Thunderbird"

Index: gc_lang/fr/rules.grx
==================================================================
--- gc_lang/fr/rules.grx
+++ gc_lang/fr/rules.grx
@@ -98,10 +98,11 @@
 # Priority: from 0 to 9. Default priority is 4.
 OPTPRIORITY/tu:     6
 OPTPRIORITY/conf:   5
 OPTPRIORITY/ocr:    3
 
+OPTDEFAULTUILANG: fr_FR
 
 # Labels
 OPTLANG/fr_FR:      Grammalecte (Français)
 OPTLABEL/basic:     Typographie
 OPTLABEL/typo:      Signes typographiques

Index: gc_lang/fr/webext/panel/main.css
==================================================================
--- gc_lang/fr/webext/panel/main.css
+++ gc_lang/fr/webext/panel/main.css
@@ -120,13 +120,10 @@
 #page h1 {
     margin: 0 0 10px 0;
     color: hsl(210, 70%, 70%);
     font: bold 30px 'Yanone Kaffeesatz', "Liberation Sans Narrow", sans-serif;
 }
-#page p {
-    margin: 10px 0 5px 0;
-}
 
 
 /*
     Home
 */
@@ -133,13 +130,10 @@
 #home_page {
     display: block;
     background-color: hsl(210, 20%, 92%);
     min-height: 100%;
 }
-#home_page p {
-    margin: 0;
-}
 #home_page #mainlogo {
     padding: 5px 20px 20px 20px;
     background-color: hsl(210, 20%, 96%);
 }
 #home_page .notice {
@@ -168,11 +162,38 @@
     Grammar checking options
 */
 #gc_options_page {
     display: none;
     padding: 20px;
-    background-color: hsl(0, 50%, 90%);
+}
+.opt_subsection {
+    margin: 5px 0;
+    padding: 10px;
+    background-color: hsl(210, 20%, 92%);
+    border-radius: 3px;
+}
+.opt_subsection h2 {
+    color: hsl(210, 30%, 50%);
+    margin-bottom: 3px;
+    font-size: 16px;
+    font-family: "Trebuchet MS", sans-serif;
+}
+.opt_subsection p {
+    padding: 2px 3px;
+    display: flex;
+    align-items: center;
+}
+.opt_subsection p:hover {
+    background-color: hsl(210, 20%, 86%);
+    border-radius: 2px;
+}
+.opt_subsection label {
+    flex: 1;
+    font-size: 12px;
+}
+.opt_subsection input {
+    order: 1
 }
 
 
 /*
     Spell checking options
@@ -179,13 +200,10 @@
 */
 #sc_options_page {
     display: none;
     padding: 20px;
 }
-#sc_options_page p {
-    margin: 0;
-}
 #dictionaries_info {
     margin: 10px 0;
     padding: 10px;
     border-radius: 3px;
     background-color: hsl(0, 50%, 40%);

Index: gc_lang/fr/webext/panel/main.html
==================================================================
--- gc_lang/fr/webext/panel/main.html
+++ gc_lang/fr/webext/panel/main.html
@@ -75,11 +75,11 @@
         </section> <!-- #help_page -->
 
         <section id="gc_options_page" class="page">
           <h1>OPTIONS GRAMMATICALES</h1>
           <div id="grammar_options">
-            ${optionsHTML}
+            ${webextOptionsHTML}
           </div>
           <p class="center" style="margin: 10px 0;"><a id="default_options" href="#" onclick="return false;">Options par défaut</a></p>
         </section> <!-- #gc_options_page -->
 
         <section id="sc_options_page" class="page">