diff --git a/build/README.md b/build/README.md
deleted file mode 100644
index bb970aa9..00000000
--- a/build/README.md
+++ /dev/null
@@ -1,13 +0,0 @@
-This is a built version of most of the extensions in this repository. It excludes:
-
-* webpack-modules: because this one is all about building the module using webpack
-
-Because the extensions mostly have no application id, they can be signed by anyone on addons.mozilla.org. We haven't checked in or stored those ids so you can rebuild them if you'd like. We don't expect end users to be expecting these examples to update automatically (which is what the id is for).
-
-A couple do have ids. You can still sign them yourself by changing the application id. If you'd like to sign them officially and add them to this repo, contact @andymckay or @wbamberg and they can do it for you.
-
-If an extension changes and you'd like to rebuild it, then you should probably update the version number before building it.
-
-To build a new version of the extension use the web-ext sign command, for example:
-
-    pushd ../commands/ && web-ext sign --artifacts-dir ../build && popd
diff --git a/build/apply_css-1.0-an+fx.xpi b/build/apply_css-1.0-an+fx.xpi
deleted file mode 100644
index 7830608a..00000000
Binary files a/build/apply_css-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/beastify-1.0-an+fx.xpi b/build/beastify-1.0-an+fx.xpi
deleted file mode 100644
index 23a317fc..00000000
Binary files a/build/beastify-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/bookmark_it-1.0-an+fx.xpi b/build/bookmark_it-1.0-an+fx.xpi
deleted file mode 100644
index cea19a0b..00000000
Binary files a/build/bookmark_it-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/borderify-1.0-an+fx.xpi b/build/borderify-1.0-an+fx.xpi
deleted file mode 100644
index 365ba759..00000000
Binary files a/build/borderify-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/chillout_page_action-1.0-an+fx.xpi b/build/chillout_page_action-1.0-an+fx.xpi
deleted file mode 100644
index a71dd015..00000000
Binary files a/build/chillout_page_action-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/context_menu_demo-1.0-an+fx.xpi b/build/context_menu_demo-1.0-an+fx.xpi
deleted file mode 100644
index 4fd3d23a..00000000
Binary files a/build/context_menu_demo-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/cookie_bg_picker-1.0-an+fx.xpi b/build/cookie_bg_picker-1.0-an+fx.xpi
deleted file mode 100644
index 24abd968..00000000
Binary files a/build/cookie_bg_picker-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/emoji_substitution-1.0-an+fx.xpi b/build/emoji_substitution-1.0-an+fx.xpi
deleted file mode 100644
index 3e1a2c83..00000000
Binary files a/build/emoji_substitution-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/eslint_example-1.0-an+fx.xpi b/build/eslint_example-1.0-an+fx.xpi
deleted file mode 100644
index 2388674b..00000000
Binary files a/build/eslint_example-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/favourite_colour-1.0-an+fx.xpi b/build/favourite_colour-1.0-an+fx.xpi
deleted file mode 100644
index 3b10bae4..00000000
Binary files a/build/favourite_colour-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/favourite_colour-1.1-an+fx.xpi b/build/favourite_colour-1.1-an+fx.xpi
deleted file mode 100644
index 1982a588..00000000
Binary files a/build/favourite_colour-1.1-an+fx.xpi and /dev/null differ
diff --git a/build/history_deleter-1.0-an+fx.xpi b/build/history_deleter-1.0-an+fx.xpi
deleted file mode 100644
index 080423c8..00000000
Binary files a/build/history_deleter-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/latest_download-1.0-an+fx.xpi b/build/latest_download-1.0-an+fx.xpi
deleted file mode 100644
index 68d2f3ce..00000000
Binary files a/build/latest_download-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/list_cookies-1.0-an+fx.xpi b/build/list_cookies-1.0-an+fx.xpi
deleted file mode 100644
index a34037a3..00000000
Binary files a/build/list_cookies-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/navigation_stats-0.1.0-an+fx.xpi b/build/navigation_stats-0.1.0-an+fx.xpi
deleted file mode 100644
index c62dc93e..00000000
Binary files a/build/navigation_stats-0.1.0-an+fx.xpi and /dev/null differ
diff --git a/build/notify_link_clicks_i18n-1.0-an+fx.xpi b/build/notify_link_clicks_i18n-1.0-an+fx.xpi
deleted file mode 100644
index 596b053c..00000000
Binary files a/build/notify_link_clicks_i18n-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/open_my_page-1.0-an+fx.xpi b/build/open_my_page-1.0-an+fx.xpi
deleted file mode 100644
index 9f7bcfda..00000000
Binary files a/build/open_my_page-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/page_to_extension_messaging-1.0-an+fx.xpi b/build/page_to_extension_messaging-1.0-an+fx.xpi
deleted file mode 100644
index 476532f2..00000000
Binary files a/build/page_to_extension_messaging-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/page_to_extension_messaging-1.0-fx.xpi b/build/page_to_extension_messaging-1.0-fx.xpi
deleted file mode 100644
index c73a0045..00000000
Binary files a/build/page_to_extension_messaging-1.0-fx.xpi and /dev/null differ
diff --git a/build/quicknote-1.0-an+fx.xpi b/build/quicknote-1.0-an+fx.xpi
deleted file mode 100644
index 36de3739..00000000
Binary files a/build/quicknote-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/sample_commands_extension-1.0-an+fx.xpi b/build/sample_commands_extension-1.0-an+fx.xpi
deleted file mode 100644
index 9ed78731..00000000
Binary files a/build/sample_commands_extension-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/sample_commands_extension-1.0-fx.xpi b/build/sample_commands_extension-1.0-fx.xpi
deleted file mode 100644
index c604b5a7..00000000
Binary files a/build/sample_commands_extension-1.0-fx.xpi and /dev/null differ
diff --git a/build/selection_to_clipboard-1.0-an+fx.xpi b/build/selection_to_clipboard-1.0-an+fx.xpi
deleted file mode 100644
index b4132728..00000000
Binary files a/build/selection_to_clipboard-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/tab_strip-1.0-an+fx.xpi b/build/tab_strip-1.0-an+fx.xpi
deleted file mode 100644
index 60e37867..00000000
Binary files a/build/tab_strip-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/tabs_tabs_tabs-1.0-an+fx.xpi b/build/tabs_tabs_tabs-1.0-an+fx.xpi
deleted file mode 100644
index e913c2f1..00000000
Binary files a/build/tabs_tabs_tabs-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/user_agent_rewriter-1.0-an+fx.xpi b/build/user_agent_rewriter-1.0-an+fx.xpi
deleted file mode 100644
index 43858553..00000000
Binary files a/build/user_agent_rewriter-1.0-an+fx.xpi and /dev/null differ
diff --git a/build/window_manipulator-1.0-an+fx.xpi b/build/window_manipulator-1.0-an+fx.xpi
deleted file mode 100644
index 04350e31..00000000
Binary files a/build/window_manipulator-1.0-an+fx.xpi and /dev/null differ
diff --git a/favourite-colour/options.js b/favourite-colour/options.js
index e3cf8254..542fa1e9 100644
--- a/favourite-colour/options.js
+++ b/favourite-colour/options.js
@@ -1,20 +1,16 @@
-function saveOptions(e) {
-  browser.storage.sync.set({
+async function saveOptions(e) {
+  e.preventDefault();
+  await browser.storage.sync.set({
     colour: document.querySelector("#colour").value
   });
-  e.preventDefault();
 }
 
-function restoreOptions() {
-  let storageItem = browser.storage.managed.get('colour');
-  storageItem.then((res) => {
-    document.querySelector("#managed-colour").innerText = res.colour;
-  });
+async function restoreOptions() {
+  let res = await browser.storage.managed.get('colour');
+  document.querySelector("#managed-colour").innerText = res.colour;
 
-  let gettingItem = browser.storage.sync.get('colour');
-  gettingItem.then((res) => {
-    document.querySelector("#colour").value = res.colour || 'Firefox red';
-  });
+  res = await browser.storage.sync.get('colour');
+  document.querySelector("#colour").value = res.colour || 'Firefox red';
 }
 
 document.addEventListener('DOMContentLoaded', restoreOptions);
diff --git a/root-cert-stats/background.js b/root-cert-stats/background.js
index 272fedad..24edf50e 100644
--- a/root-cert-stats/background.js
+++ b/root-cert-stats/background.js
@@ -1,6 +1,9 @@
 "use strict";
 
-let rootCertStats = {};
+// Note: declared with "var" because popup.js references this global variable.
+// If this were to be declared with "const" or "let", then the variable would
+// still be available to this file, but not to popup.js.
+var rootCertStats = {};
 
 /*
 On an onHeadersReceived event, if there was a successful TLS connection