diff --git a/package-lock.json b/package-lock.json
index 6300ca5..807d2ca 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -19,7 +19,7 @@
         "eslint-plugin-mozilla": "4.4.0",
         "eslint-plugin-no-unsanitized": "4.1.5",
         "jest": "^30.0.0",
-        "npm-run-all2": "9.0.2",
+        "npm-run-all2": "9.0.3",
         "prettier": "3.9.6",
         "rimraf": "6.1.3",
         "selenium-webdriver": "^4.20.0",
@@ -7499,12 +7499,12 @@
       }
     },
     "node_modules/npm-run-all2": {
-      "version": "9.0.2",
-      "resolved": "https://registry.npmjs.org/npm-run-all2/-/npm-run-all2-9.0.2.tgz",
-      "integrity": "sha512-+dd4SO2jAlLE06OzmJKzIe6QvvjXezcbmobnh8usR0a8BzQCABTdqTXqVPji0ICOhSQpIIrkGd7IzNl5iDaRSA==",
+      "version": "9.0.3",
+      "resolved": "https://registry.npmjs.org/npm-run-all2/-/npm-run-all2-9.0.3.tgz",
+      "integrity": "sha512-BQAEdU1PtYc48qYRdghW2BVTQT3VqWCoFQmO87NlM1h1PYwMCKQpUWaNyB20V26caNzFsXQDfyOdznLlHCih6g==",
       "dev": true,
       "dependencies": {
-        "ansi-styles": "^6.2.1",
+        "ansi-styles": "^7.0.0",
         "cross-spawn": "^7.0.6",
         "memorystream": "^0.3.1",
         "picomatch": "^4.0.2",
@@ -7525,12 +7525,12 @@
       }
     },
     "node_modules/npm-run-all2/node_modules/ansi-styles": {
-      "version": "6.2.3",
-      "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-6.2.3.tgz",
-      "integrity": "sha512-4Dj6M28JB+oAH8kFkTLUo+a2jwOFkuqb3yucU0CANcRRUbxS0cP0nZYCGjcc3BNXwRIsUVmDGgzawme7zvJHvg==",
+      "version": "7.0.0",
+      "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-7.0.0.tgz",
+      "integrity": "sha512-kKvt3m4uwzqL0wlkPd09CmljPJGOZZ4D0fP65sqFSvPkMRKhNi+74MgIJ5QxE6SxqB4t4KyUFGg8+n5zjo6hew==",
       "dev": true,
       "engines": {
-        "node": ">=12"
+        "node": ">=22"
       },
       "funding": {
         "url": "https://github.com/chalk/ansi-styles?sponsor=1"
@@ -7557,18 +7557,6 @@
         "url": "https://github.com/sponsors/jonschlinkert"
       }
     },
-    "node_modules/npm-run-all2/node_modules/shell-quote": {
-      "version": "1.10.0",
-      "resolved": "https://registry.npmjs.org/shell-quote/-/shell-quote-1.10.0.tgz",
-      "integrity": "sha512-w1aiOKwKuRgtwAReIIj89puqg+I7GvX4IbLrvmhXbzQsj1+Zwi4VO3+fa6ZF91TWSjIxoEkKnMeHcLEODK5ZXA==",
-      "dev": true,
-      "engines": {
-        "node": ">= 0.4"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/ljharb"
-      }
-    },
     "node_modules/npm-run-all2/node_modules/which": {
       "version": "7.0.0",
       "resolved": "https://registry.npmjs.org/which/-/which-7.0.0.tgz",
@@ -15933,12 +15921,12 @@
       "dev": true
     },
     "npm-run-all2": {
-      "version": "9.0.2",
-      "resolved": "https://registry.npmjs.org/npm-run-all2/-/npm-run-all2-9.0.2.tgz",
-      "integrity": "sha512-+dd4SO2jAlLE06OzmJKzIe6QvvjXezcbmobnh8usR0a8BzQCABTdqTXqVPji0ICOhSQpIIrkGd7IzNl5iDaRSA==",
+      "version": "9.0.3",
+      "resolved": "https://registry.npmjs.org/npm-run-all2/-/npm-run-all2-9.0.3.tgz",
+      "integrity": "sha512-BQAEdU1PtYc48qYRdghW2BVTQT3VqWCoFQmO87NlM1h1PYwMCKQpUWaNyB20V26caNzFsXQDfyOdznLlHCih6g==",
       "dev": true,
       "requires": {
-        "ansi-styles": "^6.2.1",
+        "ansi-styles": "^7.0.0",
         "cross-spawn": "^7.0.6",
         "memorystream": "^0.3.1",
         "picomatch": "^4.0.2",
@@ -15949,9 +15937,9 @@
       },
       "dependencies": {
         "ansi-styles": {
-          "version": "6.2.3",
-          "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-6.2.3.tgz",
-          "integrity": "sha512-4Dj6M28JB+oAH8kFkTLUo+a2jwOFkuqb3yucU0CANcRRUbxS0cP0nZYCGjcc3BNXwRIsUVmDGgzawme7zvJHvg==",
+          "version": "7.0.0",
+          "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-7.0.0.tgz",
+          "integrity": "sha512-kKvt3m4uwzqL0wlkPd09CmljPJGOZZ4D0fP65sqFSvPkMRKhNi+74MgIJ5QxE6SxqB4t4KyUFGg8+n5zjo6hew==",
           "dev": true
         },
         "isexe": {
@@ -15966,12 +15954,6 @@
           "integrity": "sha512-RvwwcruNjI1ncT5xRakeyS9Lf8lcItv34KD+aif+VH9kduAyfYBipGh12274xtenIPZ119/R9BdTBa8gAwSh0A==",
           "dev": true
         },
-        "shell-quote": {
-          "version": "1.10.0",
-          "resolved": "https://registry.npmjs.org/shell-quote/-/shell-quote-1.10.0.tgz",
-          "integrity": "sha512-w1aiOKwKuRgtwAReIIj89puqg+I7GvX4IbLrvmhXbzQsj1+Zwi4VO3+fa6ZF91TWSjIxoEkKnMeHcLEODK5ZXA==",
-          "dev": true
-        },
         "which": {
           "version": "7.0.0",
           "resolved": "https://registry.npmjs.org/which/-/which-7.0.0.tgz",
diff --git a/package.json b/package.json
index 2445a16..86a32a5 100644
--- a/package.json
+++ b/package.json
@@ -34,7 +34,7 @@
     "eslint-plugin-no-unsanitized": "4.1.5",
     "prettier": "3.9.6",
     "jest": "^30.0.0",
-    "npm-run-all2": "9.0.2",
+    "npm-run-all2": "9.0.3",
     "rimraf": "6.1.3",
     "selenium-webdriver": "^4.20.0",
     "web-ext": "10.5.0"
diff --git a/tests/selenium.spec.js b/tests/selenium.spec.js
index 0b596c4..06c924a 100644
--- a/tests/selenium.spec.js
+++ b/tests/selenium.spec.js
@@ -1,5 +1,9 @@
 const { Browser, Builder, By } = require("selenium-webdriver");
-const { Context, Options } = require("selenium-webdriver/firefox");
+const {
+  Context,
+  Options,
+  ServiceBuilder,
+} = require("selenium-webdriver/firefox");
 const FirefoxProfile = require("firefox-profile");
 const path = require("path");
 
@@ -23,9 +27,6 @@ beforeAll(async () => {
   options.setBinary(process.env.NIGHTLY_PATH || "/usr/bin/firefox-nightly");
   options.addArguments("--pref 'extensions.experiments.enabled=true'");
   options.addArguments("--headless");
-  // Required to switch WebDriver into the privileged chrome context, which we
-  // use to resolve the extension's moz-extension:// URL below.
-  options.addArguments("-remote-allow-system-access");
   options.setPreference("xpinstall.signatures.required", false);
   options.setPreference("extensions.experiments.enabled", true);
   options.setPreference(
@@ -35,9 +36,16 @@ beforeAll(async () => {
     }),
   );
 
+  // Switching WebDriver into the privileged chrome context (see below) requires
+  // system access. Firefox rejects `-remote-allow-system-access` when it is
+  // passed through capabilities, so it has to be enabled on the geckodriver
+  // process itself.
+  const service = new ServiceBuilder().addArguments("--allow-system-access");
+
   driver = await new Builder()
     .forBrowser(Browser.FIREFOX)
     .setFirefoxOptions(options)
+    .setFirefoxService(service)
     .build();
 
   // install the addon