It wasn't obvious how to attach this patch in bugzilla, or on the command line, so I'm using this secret gist for now.

1014090.patch

# HG changeset patch
# User Chris Adams <chris@productscience.co.uk>
# Date 1526983200 -7200
#      Tue May 22 12:00:00 2018 +0200
# Node ID 478f9211661aaefef2ff2a8d56b91f1163db0f8b
# Parent  dc1868d255be744a7d2d462216be205086cc60af
Bug 1014090 - Toggle inspector on mac with extra cmd+shift+C shortcut

diff --git a/devtools/client/definitions.js b/devtools/client/definitions.js
--- a/devtools/client/definitions.js
+++ b/devtools/client/definitions.js
@@ -73,9 +73,15 @@ Tools.inspector = {
   label: l10n("inspector.label"),
   panelLabel: l10n("inspector.panelLabel"),
   get tooltip() {
-    return l10n("inspector.tooltip2",
-    (osString == "Darwin" ? "Cmd+Opt+" : "Ctrl+Shift+") +
-    l10n("inspector.commandkey"));
+    if (osString == "Darwin") {
+      let ctrlShiftC = "Ctrl+Shift+" + l10n("inspector.commandkey");
+      let cmdOptC = "Cmd+Opt+" + l10n("inspector.commandkey");
+      return l10n("inspector.mac.tooltip", ctrlShiftC, cmdOptC);
+    } else {
+      return l10n("inspector.tooltip2", "Ctrl+Shift+") + l10n("inspector.commandkey");
+    }
+
+
   },
   inMenu: true,
   commands: [
@@ -624,9 +630,9 @@ exports.ToolboxButtons = [
  *        Optional format argument.
  * @returns A localized version of the given key.
  */
-function l10n(name, arg) {
+function l10n(name, ...args) {
   try {
-    return arg ? L10N.getFormatStr(name, arg) : L10N.getStr(name);
+    return args ? L10N.getFormatStr(name, ...args) : L10N.getStr(name);
   } catch (ex) {
     console.log("Error reading '" + name + "'");
     throw new Error("l10n error with " + name);
diff --git a/devtools/client/locales/en-US/startup.properties b/devtools/client/locales/en-US/startup.properties
--- a/devtools/client/locales/en-US/startup.properties
+++ b/devtools/client/locales/en-US/startup.properties
@@ -154,6 +154,10 @@ inspector.panelLabel=Inspector Panel
 # Keyboard shortcut for DOM and Style Inspector will be shown inside brackets.
 inspector.tooltip2=DOM and Style Inspector (%S)
 
+# LOCALIZATION NOTE (inspector.tooltip2)
+# On a mac only, we support toggling the inspector with either cmd+shift+C or cmd+opt+C
+inspector.mac.tooltip=DOM and Style Inspector (%1$S or %2$S)
+
 # LOCALIZATION NOTE (netmonitor.label):
 # This string is displayed in the title of the tab when the Network Monitor is
 # displayed inside the developer tools window and in the Developer Tools Menu.
diff --git a/devtools/startup/devtools-startup.js b/devtools/startup/devtools-startup.js
--- a/devtools/startup/devtools-startup.js
+++ b/devtools/startup/devtools-startup.js
@@ -69,7 +69,7 @@ XPCOMUtils.defineLazyGetter(this, "KeySh
 
   // List of all key shortcuts triggering installation UI
   // `id` should match tool's id from client/definitions.js
-  return [
+  let shortCuts = [
     // The following keys are also registered in /client/menus.js
     // And should be synced.
 
@@ -169,6 +169,17 @@ XPCOMUtils.defineLazyGetter(this, "KeySh
       modifiers
     },
   ];
+
+  if (isMac) {
+    // add the extra key command, so you can open the inspector with cmd+shift+C, like chrome
+    shortCuts.push({
+      toolId: "inspector",
+      shortcut: KeyShortcutsBundle.GetStringFromName("inspector.commandkey"),
+      modifiers: "accel,shift"
+    });
+  }
+  return shortCuts;
+
 });
 
 function DevToolsStartup() {

my.attempt.at.submitting.with.hg.md

Ok,

I've tried both ways to attach a patch as listed below:

https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/How_to_Submit_a_Patch#Submitting_the_patch

Submitting through bugzilla

It might be staring me in the face, but I couldn't see any text, link or button along the lines of 'add an attachment' as outlined in the docs.

Submitting through mercurial

Here's the output from when I tried to set up mercurial to attach patches from the command line:"

~/C/m/mozilla-central ❯❯❯ ./mach mercurial-setup                                                                                     ⏎
================================================================================
Ensuring https://hg.mozilla.org/hgcustom/version-control-tools is up to date at /Users/chrisadams/.mozbuild/version-control-tools
pulling from https://hg.mozilla.org/hgcustom/version-control-tools
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 3 changes to 3 files
updating bookmark @
new changesets 64e8a28c6208
(run 'hg update' to get a working copy)
3 files updated, 0 files merged, 0 files removed, 0 files unresolved
================================================================================
This wizard will guide you through configuring Mercurial for an optimal
experience contributing to Mozilla projects.

The wizard makes no changes without your permission.

To begin, press the enter/return key.


It looks like the setup wizard has already installed a copy of the
evolve extension on your machine, at /Users/chrisadams/.mozbuild/evolve.

(Relevant config option: extensions.evolve)

Would you like to update evolve to the latest version?  (Yn)
pulling from https://www.mercurial-scm.org/repo/evolve/
no changes found
16010 new obsolescence markers
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
Evolve was updated successfully.

Okay, this looks promising. Let's see what happens when we try running that bzexport command:

~/C/m/mozilla-central ❯❯❯ hg bzexport -e
hg: unknown command 'bzexport'
(did you mean export?)

Oh. What did I do wrong here?