diff --git a/src/__tests__/posthog-persistence.test.ts b/src/__tests__/posthog-persistence.test.ts
index 4f956459a..e80fb4614 100644
--- a/src/__tests__/posthog-persistence.test.ts
+++ b/src/__tests__/posthog-persistence.test.ts
@@ -1,6 +1,6 @@
 /// <reference lib="dom" />
 import { PostHogPersistence } from '../posthog-persistence'
-import { SESSION_ID, USER_STATE } from '../constants'
+import { CLIENT_SESSION_PROPS, SESSION_ID, USER_STATE } from '../constants'
 import { PostHogConfig } from '../types'
 import Mock = jest.Mock
 
@@ -18,7 +18,7 @@ describe('persistence', () => {
     let library: PostHogPersistence
 
     afterEach(() => {
-        library.clear()
+        library?.clear()
         document.cookie = ''
         referrer = ''
     })
@@ -139,6 +139,7 @@ describe('persistence', () => {
                     distinct_id: 'test',
                 })}`
             )
+            expect(document.cookie).not.toContain('test_prop')
 
             lib.register({ otherProp: 'prop' })
             expect(document.cookie).toContain(
@@ -155,6 +156,29 @@ describe('persistence', () => {
                 })}`
             )
 
+            lib.register({
+                [CLIENT_SESSION_PROPS]: {
+                    sessionId: 'sid',
+                    props: {
+                        initialPathName: '/some/pathname',
+                        referringDomain: '$direct',
+                    },
+                },
+            })
+            expect(document.cookie).toContain(
+                `ph__posthog=${encode({
+                    distinct_id: 'test',
+                    $sesid: [1000, 'sid', 2000],
+                    $client_session_props: {
+                        sessionId: 'sid',
+                        props: {
+                            initialPathName: '/some/pathname',
+                            referringDomain: '$direct',
+                        },
+                    },
+                })}`
+            )
+
             // Clear localstorage to simulate being on a different domain
             localStorage.clear()
 
@@ -163,6 +187,13 @@ describe('persistence', () => {
             expect(newLib.props).toEqual({
                 distinct_id: 'test',
                 $sesid: [1000, 'sid', 2000],
+                $client_session_props: {
+                    sessionId: 'sid',
+                    props: {
+                        initialPathName: '/some/pathname',
+                        referringDomain: '$direct',
+                    },
+                },
             })
         })
     })
diff --git a/src/posthog-core.ts b/src/posthog-core.ts
index b3eb68e90..55ea3f212 100644
--- a/src/posthog-core.ts
+++ b/src/posthog-core.ts
@@ -108,7 +108,7 @@ export const defaultConfig = (): PostHogConfig => ({
     autocapture: true,
     rageclick: true,
     cross_subdomain_cookie: isCrossDomainCookie(document?.location),
-    persistence: 'cookie',
+    persistence: 'localStorage+cookie', // up to 1.92.0 this was 'cookie'. It's easy to migrate as 'localStorage+cookie' will migrate data from cookie storage
     persistence_name: '',
     cookie_name: '',
     loaded: __NOOP,
diff --git a/src/posthog-persistence.ts b/src/posthog-persistence.ts
index 7ccbec21f..71017e659 100644
--- a/src/posthog-persistence.ts
+++ b/src/posthog-persistence.ts
@@ -64,8 +64,10 @@ export class PostHogPersistence {
                 config['persistence'].toLowerCase() as Lowercase<PostHogConfig['persistence']>
             ) === -1
         ) {
-            logger.critical('Unknown persistence type ' + config['persistence'] + '; falling back to cookie')
-            config['persistence'] = 'cookie'
+            logger.critical(
+                'Unknown persistence type ' + config['persistence'] + '; falling back to localStorage+cookie'
+            )
+            config['persistence'] = 'localStorage+cookie'
         }
         // We handle storage type in a case-insensitive way for backwards compatibility
         const storage_type = config['persistence'].toLowerCase() as Lowercase<PostHogConfig['persistence']>
@@ -77,8 +79,15 @@ export class PostHogPersistence {
             this.storage = sessionStore
         } else if (storage_type === 'memory') {
             this.storage = memoryStore
-        } else {
+        } else if (storage_type === 'cookie') {
             this.storage = cookieStore
+        } else {
+            // selected storage type wasn't supported, fallback to 'localstorage+cookie' if possible
+            if (localPlusCookieStore.is_supported()) {
+                this.storage = localPlusCookieStore
+            } else {
+                this.storage = cookieStore
+            }
         }
 
         this.user_state = 'anonymous'
diff --git a/src/session-props.ts b/src/session-props.ts
index 79021ae80..48bced994 100644
--- a/src/session-props.ts
+++ b/src/session-props.ts
@@ -12,7 +12,7 @@ import { SessionIdManager } from './sessionid'
 import { PostHogPersistence } from './posthog-persistence'
 import { CLIENT_SESSION_PROPS } from './constants'
 
-interface SessionSourceProps {
+export interface SessionSourceProps {
     initialPathName: string
     referringDomain: string // Is actually host, but named domain for internal consistency. Should contain a port if there is one.
     utm_medium?: string
@@ -22,7 +22,7 @@ interface SessionSourceProps {
     utm_term?: string
 }
 
-interface StoredSessionSourceProps {
+export interface StoredSessionSourceProps {
     sessionId: string
     props: SessionSourceProps
 }
diff --git a/src/storage.ts b/src/storage.ts
index c559b379c..b090e5892 100644
--- a/src/storage.ts
+++ b/src/storage.ts
@@ -1,6 +1,6 @@
 import { _extend } from './utils'
 import { PersistentStore, Properties } from './types'
-import { DISTINCT_ID, SESSION_ID, SESSION_RECORDING_IS_SAMPLED } from './constants'
+import { CLIENT_SESSION_PROPS, DISTINCT_ID, SESSION_ID, SESSION_RECORDING_IS_SAMPLED } from './constants'
 
 import { _isNull, _isUndefined } from './utils/type-utils'
 import { logger } from './utils/logger'
@@ -140,6 +140,12 @@ export const cookieStore: PersistentStore = {
                 '; SameSite=Lax; path=/' +
                 cdomain +
                 secure
+
+            // 4096 bytes is the size at which some browsers (e.g. firefox) will not store a cookie, warn slightly before that
+            if (new_cookie_val.length > 4096 * 0.9) {
+                logger.warn('cookieStore warning: large cookie, len=' + new_cookie_val.length)
+            }
+
             document.cookie = new_cookie_val
             return new_cookie_val
         } catch (err) {
@@ -230,7 +236,7 @@ export const localStore: PersistentStore = {
 // Use localstorage for most data but still use cookie for COOKIE_PERSISTED_PROPERTIES
 // This solves issues with cookies having too much data in them causing headers too large
 // Also makes sure we don't have to send a ton of data to the server
-const COOKIE_PERSISTED_PROPERTIES = [DISTINCT_ID, SESSION_ID, SESSION_RECORDING_IS_SAMPLED]
+const COOKIE_PERSISTED_PROPERTIES = [DISTINCT_ID, SESSION_ID, SESSION_RECORDING_IS_SAMPLED, CLIENT_SESSION_PROPS]
 
 export const localPlusCookieStore: PersistentStore = {
     ...localStore,