Add spinner optional feature

This is optional because Firefox has issues rendering the spinner SVG.

Author: rafaelmardojai

README.md

@@ -168,6 +168,14 @@ Optional features can be enabled by creating new `boolean` preferences in `about
 
 	> **Note:** You should move the new tab button somewhere else for this to work, because by default it is on the tab bar too. See [#54](https://github.com/rafaelmardojai/firefox-gnome-theme/issues/54).
 
+- **Spinner** `gnomeTheme.spinner`
+
+	Use the GNOME spinner for tabs loading.
+
+	> **Note:** This is optional because Firefox has issues rendering the spinner SVG:
+	>
+	> <img src="theme/icons/process-working-symbolic.svg" alt="GTK Spinner" width="50"/>
+
 - **Normal width tabs** `gnomeTheme.normalWidthTabs`
 
 	Use normal width tabs as default Firefox.

theme/icons/process-working-symbolic.svg

@@ -308,6 +308,26 @@ tab[selected]:-moz-window-inactive {
 	z-index: 1;
 }
 
+/* OPTIONAL: GNOME spinner */
+/* Temporal until I find time to work around the rendering issue */
+@supports -moz-bool-pref("gnomeTheme.spinner") {
+	/* Tab spinner */
+	.tab-throbber::before {
+		animation: gnome-spinner 1s linear infinite !important;
+		background-image: url("../icons/process-working-symbolic.svg") !important;
+		width: 16px !important;
+		opacity: 1 !important;
+	}
+	@keyframes gnome-spinner {
+		from {
+			transform: rotate(0deg);
+		}
+		to {
+			transform: rotate(360deg);
+		}
+	}
+}
+
 /* OPTIONAL: Hide single tab */
 @supports -moz-bool-pref("gnomeTheme.hideSingleTab") {
 	#tabbrowser-tabs tab:only-of-type {
@@ -330,4 +350,3 @@ tab[selected]:-moz-window-inactive {
 		background: var(--gnome-tabbar-tab-active-background-contrast) !important;
 	}
 }
-