🐛 Hide the custom resize icon of the plugin modal in Firefox (#11798)

Firefox draws its own resize grip for a box with `resize: both` and,
unlike Chrome and Safari, gives no way to hide it: `::-webkit-resizer`
is ignored. The plugin modal therefore showed two grips in its
bottom-right corner, its own icon and the one from the browser.

Show the custom icon only where the browser grip can be hidden. In
Firefox the native grip is now the only one.

Closes #11795

plugins/CHANGELOG.md

@@ -14,6 +14,7 @@
 - **plugins-runtime**: `Library.createComponent()` now rejects invalid input (an empty shape list, or a shape inside a component copy) with a validation error instead of returning a component proxy pointing at nothing.
 - **plugins-runtime**: Setting an individual padding/margin side (`leftPadding`, `topMargin`, …) now re-derives the padding/margin type, switching to `multiple` when the four sides stop being symmetric (so the value is actually painted) and back to `simple` once top/bottom and left/right are mirrored again.
 - **plugins-runtime**: Removed the premature deep-hardening of the host plugin context, which froze shared host functions (including `Function.prototype`) before SES override taming, causing `TypeError: Cannot assign to read only property 'toString'` on later host-side function extension. Related to #11001.
+- **plugins-runtime**: The plugin modal no longer shows two resize grips in Firefox. Firefox now shows only its native grip. Closes #11795.
 - **plugins-runtime**: Fixed the `fontFamilies` token property mapping so `Shape.applyToken(token, ["fontFamilies"])` resolves to the canonical `:font-family` attribute and applied-token readback exposes the documented `fontFamilies` key instead of the undocumented singular `fontFamily`. Closes #11405.
 
 ## 1.5.0 (2026-07-08)

plugins/libs/plugins-runtime/src/lib/modal/plugin.modal.css

@@ -29,6 +29,13 @@
   display: none;
 }
 
+/* Firefox cannot hide its native resize grip, so show only that one. */
+@supports (-moz-appearance: none) {
+  .wrapper:after {
+    display: none;
+  }
+}
+
 .wrapper {
   position: absolute;
   inset-block-start: var(--modal-block-start);