References: 
When a particular firmware is selected, read the json file for a description.
Add a tooltip of the json description when the mouse move overs the selected firmware.

Index: virt-manager-4.1.0/virtManager/details/details.py
===================================================================
--- virt-manager-4.1.0.orig/virtManager/details/details.py
+++ virt-manager-4.1.0/virtManager/details/details.py
@@ -4,6 +4,10 @@
 # This work is licensed under the GNU GPLv2 or later.
 # See the COPYING file in the top-level directory.
 
+import os
+import json
+import textwrap
+
 from gi.repository import Gtk
 
 import libvirt
@@ -402,7 +406,7 @@ class vmmDetails(vmmGObjectUI):
             "on_overview_name_changed": _e(EDIT_NAME),
             "on_overview_title_changed": _e(EDIT_TITLE),
             "on_machine_type_changed": _e(EDIT_MACHTYPE),
-            "on_overview_firmware_changed": _e(EDIT_FIRMWARE),
+            "on_overview_firmware_changed": self._uefi_combobox_changed_cb,
             "on_overview_chipset_changed": _e(EDIT_MACHTYPE),
 
             "on_details_inspection_refresh_clicked": self._inspection_refresh_clicked_cb,
@@ -1098,6 +1102,52 @@ class vmmDetails(vmmGObjectUI):
         self.storage_browser.set_browse_reason(reason)
         self.storage_browser.show(self.topwin)
 
+    def _uefi_combobox_changed_cb(self, src):
+        def get_firmware_description(firmware_file):
+            json_description = ""
+            firmware_json_path = "/usr/share/qemu/firmware"
+            if os.path.isdir(firmware_json_path):
+                json_files = [f for f in os.listdir(firmware_json_path) if os.path.isfile(os.path.join(firmware_json_path, f))]
+                for jf in json_files:
+                    full_path = firmware_json_path + '/' + jf
+                    if not full_path.endswith(".json"):
+                        continue
+                    try:
+                        if os.stat(full_path).st_size > 65536:
+                            continue
+                    except OSError:
+                        continue
+                    with open(full_path, 'r') as json_file:
+                        data = json_file.read()
+                    try:
+                        json_obj = json.loads(data)
+                    except Exception as e:
+                        continue
+                    if 'mapping' in json_obj and 'executable' in json_obj['mapping']:
+                        json_exec = str(json_obj['mapping']['executable']['filename'])
+                        if json_exec == firmware_file:
+                            json_description = str(json_obj['description'])
+                            json_features = str(json_obj['features'])
+                            if len(json_features) > 0:
+                                json_description = json_description + ". Firmware features: " + json_features
+                            wrapper = textwrap.TextWrapper(width=60)
+                            json_list = wrapper.wrap(text=json_description)
+                            json_description = "\n".join(json_list)
+                            break
+            return json_description
+
+        combo = self.widget("overview-firmware")
+        tree_iter = combo.get_active_iter()
+        if tree_iter is not None:
+            model = combo.get_model()
+            tooltip_text = ""
+            firmware = model[tree_iter][0]
+            if firmware != 'BIOS':
+                firmware_file = firmware.split()[-1]
+                tooltip_text = get_firmware_description(firmware_file)
+            combo.set_tooltip_text(tooltip_text)
+        self._enable_apply(EDIT_FIRMWARE)
+
     def _inspection_refresh_clicked_cb(self, src):
         from ..lib.inspection import vmmInspection
         inspection = vmmInspection.get_instance()