diff --git a/.dockerignore b/.dockerignore
index 951e486d..e3c038d8 100644
--- a/.dockerignore
+++ b/.dockerignore
@@ -15,6 +15,7 @@ tests/*
 !tests/frontend-compat.test.mjs
 !tests/block-selection.test.mjs
 !tests/datepicker-compat.test.mjs
+!tests/preview-url.test.mjs
 !tests/vite-compat.test.mjs
 docs
 vendor
diff --git a/_dev/src/components/Iframe.vue b/_dev/src/components/Iframe.vue
index 780b94b2..c5292261 100644
--- a/_dev/src/components/Iframe.vue
+++ b/_dev/src/components/Iframe.vue
@@ -35,6 +35,9 @@ let currentPrettyBlocksId = computed(() => currentBlock.id_prettyblocks)
  */
 onMounted(() => {
   prettyBlocksContext.setIframe()
+  if (new URL(window.location.href).searchParams.has('startup_url')) {
+    prettyBlocksContext.pushUrl(prettyBlocksContext.psContext.current_url)
+  }
 })
 
 watch(currentBlock, (newVal, oldValue) => {
@@ -51,11 +54,7 @@ const reloadIframe = () => {
 }
 
 
-let filteredURL = ref(prettyBlocksContext.updateFilteredURL(ajax_urls.startup_url))
-
-watch(prettyBlocksContext.psContext, () => {
-  filteredURL.value = prettyBlocksContext.updateFilteredURL(prettyBlocksContext.psContext.current_url)
-})
+const filteredURL = computed(() => prettyBlocksContext.psContext.current_url)
 </script>
 
 <template>
diff --git a/_dev/src/components/form/ShopSelect.vue b/_dev/src/components/form/ShopSelect.vue
index 91e0f89a..c0535389 100644
--- a/_dev/src/components/form/ShopSelect.vue
+++ b/_dev/src/components/form/ShopSelect.vue
@@ -23,17 +23,19 @@ const props = defineProps({
 
 const changetItem = (item) => {
   props.modelValue.shop_name = item.name
+  const { id_lang, id_shop } = prettyBlocksContext.psContext
 
   prettyBlocksContext.$patch({
     psContext: {
       id_lang: item.id_lang,
       id_shop: item.id_shop,
       shop_name: item.name,
-      current_url: item.base_url + (item.base_url.includes('?prettyblocks=1') ? '' : '?prettyblocks=1'),
       href: item.base_url,
     }
   })
-  prettyBlocksContext.changeUrl(item.base_url)
+  prettyBlocksContext.changeUrl(item.base_url, {
+    reloadSame: id_lang !== item.id_lang || id_shop !== item.id_shop,
+  })
 }
 
 const emit = defineEmits(['update:modelValue.shop_name'])
diff --git a/_dev/src/scripts/eventHandler.js b/_dev/src/scripts/eventHandler.js
index 694d6219..701d8741 100644
--- a/_dev/src/scripts/eventHandler.js
+++ b/_dev/src/scripts/eventHandler.js
@@ -19,22 +19,12 @@ export const eventHandler = async (event) => {
                 })
             }
            
-            if(event.data.type == 'setNewUrl' || event.data.type == 'setForceNewUrl')
-                {  
-                    let context = event.data.params.context
-                    let custom_url = event.data.params.url
-                    let force_reload = event.data.type == 'setForceNewUrl' ? true : false
-                            
-                    
-                    prettyBlocksContext.$patch({
-                        psContext: {
-                        ...prettyBlocksContext.psContext,
-                        ...context,
-                        current_url: custom_url
-                    }
-                });
-                prettyBlocksContext.changeUrl(custom_url)
-                if(force_reload) {
+            if (event.data.type == 'setNewUrl' || event.data.type == 'setForceNewUrl') {
+                const { context, url } = event.data.params
+                const { id_lang, id_shop, shop_name, href } = context
+                prettyBlocksContext.$patch({ psContext: { id_lang, id_shop, shop_name, href } })
+                const navigated = prettyBlocksContext.changeUrl(url)
+                if (event.data.type == 'setForceNewUrl' && navigated) {
                     window.location.reload()
                 }
             }
diff --git a/_dev/src/store/pinia.js b/_dev/src/store/pinia.js
index 829fa8ba..54757a95 100644
--- a/_dev/src/store/pinia.js
+++ b/_dev/src/store/pinia.js
@@ -4,6 +4,7 @@ import { eventHandler } from '../scripts/eventHandler'
 import { createToaster } from "@meforma/vue-toaster";
 import { HttpClient } from '../services/HttpClient';
 import { acceptsBlockRefresh, blockSelectionAfterRefresh, sameBlockContext, snapshotBlockContext } from './blockSelection.mjs';
+import { withPrettyBlocksMode } from './previewUrl.mjs';
 const toaster = createToaster({
   position: "top",
 });
@@ -47,7 +48,9 @@ export const usePrettyBlocksContext = defineStore('prettyBlocksContext', {
       id_lang: 1,
       id_shop: 1,
       shop_name: null,
-      current_url: ajax_urls.startup_url + (ajax_urls.startup_url.includes('?prettyblocks=1') ? '' : '?prettyblocks=1'),
+      current_url: withPrettyBlocksMode(ajax_urls.startup_url, ajax_urls.base_url)
+        ?? withPrettyBlocksMode(ajax_urls.base_url)
+        ?? 'about:blank',
       href: ajax_urls.startup_url,
     },
     iframe: {
@@ -196,16 +199,25 @@ export const usePrettyBlocksContext = defineStore('prettyBlocksContext', {
       let message = { type: eventType, data: data };
       this.iframe.domElement.contentWindow.postMessage(message, "*");
     },
-    changeUrl(url) {
+    changeUrl(url, { reloadSame = false } = {}) {
+      const previewUrl = this.updateFilteredURL(url)
+      if (!previewUrl) {
+        return false
+      }
+      this.pushUrl(previewUrl)
+      if (previewUrl === this.psContext.current_url) {
+        if (reloadSame) {
+          this.reloadIframe()
+        }
+        return false
+      }
       this.$patch((state) => {
-        state.psContext.current_url = this.updateFilteredURL(url)
+        state.psContext.current_url = previewUrl
       })
-      // Update the current window URL with startup_url parameter
-      this.pushUrl(url)
       this.showLoader()
       this.setIframe()
       this.emit('urlChanged', url)
-
+      return true
     },
     showLoader() {
       this.$patch((state) => {
@@ -224,29 +236,13 @@ export const usePrettyBlocksContext = defineStore('prettyBlocksContext', {
       currentUrl.searchParams.delete('id');
       currentUrl.searchParams.delete('endpoint');
 
-      currentUrl.searchParams.set('startup_url', this.updateFilteredURL(url));
-      window.history.replaceState({}, '', currentUrl.toString());
+      currentUrl.searchParams.set('startup_url', url);
+      if (currentUrl.href !== window.location.href) {
+        window.history.replaceState({}, '', currentUrl.href);
+      }
     },
     updateFilteredURL(url) {
-        if (url.startsWith('/')) {
-
-            if (ajax_urls.base_url.endsWith('/')) {
-                url = ajax_urls.base_url + url.substring(1);
-            } else {
-                url = ajax_urls.base_url + url;
-            }
-        }
-
-        let hashIndex = url.indexOf('#');
-        if (hashIndex !== -1) {
-            url = url.substring(0, hashIndex) + '?prettyblocks=1' + url.substring(hashIndex);
-        } else if (!url.includes('?')) {
-            url += '?prettyblocks=1';
-        } else if (!url.includes('prettyblocks')) {
-            url += '&prettyblocks=1';
-        }
-
-        return url;
+      return withPrettyBlocksMode(url, ajax_urls.base_url, this.psContext.href);
     },
     reloadIframe(currentSrc = false) {
       if (this.iframe.domElement) {
diff --git a/_dev/src/store/previewUrl.mjs b/_dev/src/store/previewUrl.mjs
new file mode 100644
index 00000000..7489a14f
--- /dev/null
+++ b/_dev/src/store/previewUrl.mjs
@@ -0,0 +1,29 @@
+export function withPrettyBlocksMode(value, baseUrl, currentUrl = baseUrl) {
+  if (typeof value !== 'string' || !value.trim()) {
+    return null;
+  }
+
+  try {
+    const shop = baseUrl ? new URL(baseUrl) : undefined;
+    const base = currentUrl ? new URL(currentUrl, shop) : shop;
+    const url = new URL(value, base);
+    if (url.protocol !== 'http:' && url.protocol !== 'https:') {
+      return null;
+    }
+
+    // Keep the shop-relative /path convention from #261 on subdirectory shops,
+    // without adding the shop directory twice to an already prefixed URL.
+    if (shop && url.origin === shop.origin && /^\/(?!\/)/.test(value)) {
+      const directory = shop.pathname.replace(/\/$/, '');
+      if (directory && url.pathname !== directory && !url.pathname.startsWith(directory + '/')) {
+        url.pathname = directory + url.pathname;
+      }
+    }
+
+    // Combination fragments must stay intact; the edit flag belongs to the query.
+    url.searchParams.set('prettyblocks', '1');
+    return url.href;
+  } catch {
+    return null;
+  }
+}
diff --git a/docker/release.Dockerfile b/docker/release.Dockerfile
index 85fb2b5e..0bf45861 100644
--- a/docker/release.Dockerfile
+++ b/docker/release.Dockerfile
@@ -11,8 +11,10 @@ RUN --mount=type=cache,target=/usr/local/share/.cache/yarn \
     && corepack yarn install --frozen-lockfile --non-interactive
 
 COPY _dev ./_dev
-COPY tests/block-selection.test.mjs tests/datepicker-compat.test.mjs tests/vite-compat.test.mjs ./tests/
-RUN node --test tests/block-selection.test.mjs tests/datepicker-compat.test.mjs tests/vite-compat.test.mjs \
+COPY tests/block-selection.test.mjs tests/datepicker-compat.test.mjs \
+    tests/preview-url.test.mjs tests/vite-compat.test.mjs ./tests/
+RUN node --test tests/block-selection.test.mjs tests/datepicker-compat.test.mjs \
+    tests/preview-url.test.mjs tests/vite-compat.test.mjs \
     && cd _dev && corepack yarn build
 
 
diff --git a/tests/preview-url.test.mjs b/tests/preview-url.test.mjs
new file mode 100644
index 00000000..956ef97b
--- /dev/null
+++ b/tests/preview-url.test.mjs
@@ -0,0 +1,79 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { withPrettyBlocksMode } from '../_dev/src/store/previewUrl.mjs';
+
+const shop = 'https://shop.example.test/store/';
+const product = shop + 'fr/1-1-t-shirt.html';
+const combination = '#/1-taille-s/8-couleur-blanc';
+
+test('puts edit mode before a product combination fragment and preserves the query', () => {
+  const input = product + '?campaign=summer&tag=a%26b' + combination;
+  const output = new URL(withPrettyBlocksMode(input, shop));
+
+  assert.equal(output.pathname, '/store/fr/1-1-t-shirt.html');
+  assert.equal(output.hash, combination);
+  assert.deepEqual([...output.searchParams], [
+    ['campaign', 'summer'], ['tag', 'a&b'], ['prettyblocks', '1'],
+  ]);
+});
+
+test('adding edit mode to a combination URL is idempotent across iframe reloads', () => {
+  const expected = product + '?prettyblocks=1' + combination;
+  assert.equal(withPrettyBlocksMode(product + combination, shop), expected);
+  assert.equal(withPrettyBlocksMode(expected, shop), expected);
+});
+
+test('replaces disabled, duplicated and previously corrupted edit flags', () => {
+  for (const query of [
+    '?prettyblocks=0',
+    '?prettyblocks=0&prettyblocks=1',
+    '?prettyblocks=1?prettyblocks=1?prettyblocks=1',
+  ]) {
+    const output = new URL(withPrettyBlocksMode(product + query + combination, shop));
+    assert.deepEqual(output.searchParams.getAll('prettyblocks'), ['1']);
+    assert.equal(output.hash, combination);
+  }
+});
+
+test('another query key or value containing prettyblocks is not the edit flag', () => {
+  const output = new URL(withPrettyBlocksMode(product + '?q=prettyblocks&notprettyblocks=0', shop));
+  assert.equal(output.searchParams.get('q'), 'prettyblocks');
+  assert.equal(output.searchParams.get('notprettyblocks'), '0');
+  assert.deepEqual(output.searchParams.getAll('prettyblocks'), ['1']);
+});
+
+test('resolves relative links, query-only links and fragments against the current preview', () => {
+  assert.equal(withPrettyBlocksMode('2-t-shirt.html' + combination, shop, product),
+    shop + 'fr/2-t-shirt.html?prettyblocks=1' + combination);
+  assert.equal(withPrettyBlocksMode('?id=2' + combination, shop, product),
+    product + '?id=2&prettyblocks=1' + combination);
+  assert.equal(withPrettyBlocksMode(combination, shop, product + '?id=2'),
+    product + '?id=2&prettyblocks=1' + combination);
+});
+
+test('keeps subdirectory and multishop URLs on their intended path and origin', () => {
+  const expected = product + '?prettyblocks=1' + combination;
+  assert.equal(withPrettyBlocksMode('fr/1-1-t-shirt.html' + combination, shop), expected);
+  assert.equal(withPrettyBlocksMode('/fr/1-1-t-shirt.html' + combination, shop), expected);
+  assert.equal(withPrettyBlocksMode('/store/fr/1-1-t-shirt.html' + combination, shop), expected);
+  assert.equal(withPrettyBlocksMode('//other.example.test/t-shirt.html' + combination, shop),
+    'https://other.example.test/t-shirt.html?prettyblocks=1' + combination);
+  assert.equal(withPrettyBlocksMode('https://other.example.test/t-shirt.html' + combination, shop),
+    'https://other.example.test/t-shirt.html?prettyblocks=1' + combination);
+});
+
+test('does not create an editor URL from empty, malformed or non-web targets', () => {
+  for (const input of ['', null, 'http://[invalid', 'javascript:alert(1)', 'mailto:shop@example.test']) {
+    assert.equal(withPrettyBlocksMode(input, shop), null);
+  }
+});
+
+test('a back-office startup_url round trip retains the query and combination', () => {
+  const editor = new URL(shop + 'admin/modules/prettyblocks/');
+  const preview = withPrettyBlocksMode(product + '?id=1' + combination, shop);
+  editor.searchParams.set('startup_url', preview);
+
+  const reopened = new URL(editor.href).searchParams.get('startup_url');
+  assert.equal(reopened, product + '?id=1&prettyblocks=1' + combination);
+  assert.equal(withPrettyBlocksMode(reopened, shop), reopened);
+});