diff --git a/.changeset/thick-worms-grab.md b/.changeset/thick-worms-grab.md
new file mode 100644
index 0000000000..5a4ce1b0a9
--- /dev/null
+++ b/.changeset/thick-worms-grab.md
@@ -0,0 +1,5 @@
+---
+'@lion/ui': patch
+---
+
+[core] allow browserDetection to be run in ssr context
diff --git a/.eslintrc.js b/.eslintrc.js
index bf815114b6..08e45b47e0 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -48,4 +48,7 @@ module.exports = {
       [path.resolve('./scripts/eslint-resolver.cjs')]: {},
     },
   },
+  env: {
+    es2020: true,
+  },
 };
diff --git a/packages/singleton-manager/src/SingletonManagerClass.js b/packages/singleton-manager/src/SingletonManagerClass.js
index 7cf4ae3350..e2cf3a13b0 100644
--- a/packages/singleton-manager/src/SingletonManagerClass.js
+++ b/packages/singleton-manager/src/SingletonManagerClass.js
@@ -5,7 +5,6 @@ const sym = Symbol.for('lion::SingletonManagerClassStorage');
  * In the future, we can just use globalThis directly
  * (for now, we're backwards compatible with browsers that still only use window, since we don't know all contexts singleton-manager is used in).
  */
-// eslint-disable-next-line no-undef
 const globalThisOrWindow = globalThis || window;
 export class SingletonManagerClass {
   constructor() {
diff --git a/packages/ui/components/core/src/browserDetection.js b/packages/ui/components/core/src/browserDetection.js
index 88fe85d680..e4b37df248 100644
--- a/packages/ui/components/core/src/browserDetection.js
+++ b/packages/ui/components/core/src/browserDetection.js
@@ -1,17 +1,27 @@
+import { isServer } from 'lit';
+
 /**
  * From https://stackoverflow.com/questions/4565112/javascript-how-to-find-out-if-the-user-browser-is-chrome
- * @param {string} [flavor]
+ * @param {string} [flavor='google-chrome']
  */
 function checkChrome(flavor = 'google-chrome') {
-  const isChromium = /** @type {window & { chrome?: boolean}} */ (window).chrome;
+  if (isServer) {
+    return flavor === 'google-chrome';
+  }
+
+  const isChromium = /** @type {window & { chrome?: boolean}} */ (globalThis).chrome;
+
   if (flavor === 'chromium') {
     return isChromium;
   }
-  const winNav = window.navigator;
-  const vendorName = winNav.vendor;
-  const isOpera = typeof (/** @type {window & { opr?: boolean}} */ (window).opr) !== 'undefined';
-  const isIEedge = winNav.userAgent.indexOf('Edge') > -1;
-  const isIOSChrome = winNav.userAgent.match('CriOS');
+  const winNav = globalThis.navigator;
+  const vendorName = winNav?.vendor;
+  const isOpera =
+    typeof (/** @type {window & { opr?: boolean}} */ (globalThis).opr) !== 'undefined';
+  // @ts-ignore
+  const isIEedge = globalThis.userAgent?.indexOf('Edge') > -1;
+  // @ts-ignore
+  const isIOSChrome = globalThis.userAgent?.match('CriOS');
 
   if (flavor === 'ios') {
     return isIOSChrome;
@@ -31,18 +41,18 @@ function checkChrome(flavor = 'google-chrome') {
 }
 
 export const browserDetection = {
-  isIE11: /Trident/.test(window.navigator.userAgent),
+  isIE11: /Trident/.test(globalThis.navigator?.userAgent),
   isChrome: checkChrome(),
   isIOSChrome: checkChrome('ios'),
   isChromium: checkChrome('chromium'),
-  isFirefox: navigator.userAgent.toLowerCase().indexOf('firefox') > -1,
-  isMac: navigator.appVersion.indexOf('Mac') !== -1,
-  isIOS: /iPhone|iPad|iPod/i.test(navigator.userAgent),
+  isFirefox: globalThis.navigator?.userAgent.toLowerCase().indexOf('firefox') > -1,
+  isMac: globalThis.navigator?.appVersion?.indexOf('Mac') !== -1,
+  isIOS: /iPhone|iPad|iPod/i.test(globalThis.navigator?.userAgent),
   isMacSafari:
-    navigator.vendor &&
-    navigator.vendor.indexOf('Apple') > -1 &&
-    navigator.userAgent &&
-    navigator.userAgent.indexOf('CriOS') === -1 &&
-    navigator.userAgent.indexOf('FxiOS') === -1 &&
-    navigator.appVersion.indexOf('Mac') !== -1,
+    globalThis.navigator?.vendor &&
+    globalThis.navigator?.vendor.indexOf('Apple') > -1 &&
+    globalThis.navigator?.userAgent &&
+    globalThis.navigator?.userAgent.indexOf('CriOS') === -1 &&
+    globalThis.navigator?.userAgent.indexOf('FxiOS') === -1 &&
+    globalThis.navigator?.appVersion.indexOf('Mac') !== -1,
 };