Bug 1928132: Implement dynamic Unified Search Button mode r=desktop-theme-reviewers,daleharvey,dao,tabbrowser-reviewers

Differential Revision: https://phabricator.services.mozilla.com/D228954

browser/components/urlbar/UrlbarInput.sys.mjs

@@ -3915,6 +3915,24 @@ export class UrlbarInput {
     this.logger.debug("Focus Event");
     if (!this._hideFocus) {
       this.toggleAttribute("focused", true);
+
+      // Prevent from showing USB until finishing user's operation if the focus
+      // is moved by mouse since user might select the urlbar value.
+      if (
+        lazy.UrlbarPrefs.get("usb.dynamic") &&
+        Services.focus.getLastFocusMethod(this.window) ==
+          Services.focus.FLAG_BYMOUSE &&
+        this.getAttribute("pageproxystate") == "valid"
+      ) {
+        this.toggleAttribute("usb-focus-processing", true);
+        this.window.addEventListener(
+          "mouseup",
+          () => {
+            this.removeAttribute("usb-focus-processing");
+          },
+          { once: true }
+        );
+      }
     }
 
     // If the value was trimmed, check whether we should untrim it.