Add Firefox notes about clipboardData limitations (#27713)

* Add Firefox clipboardData note about only pasting first file

* Apply suggestions from code review

---------

Co-authored-by: Claas Augner <[email protected]>

Author: ZunedKhan07

api/ClipboardEvent.json

@@ -16,7 +16,11 @@
             "version_added": "12"
           },
           "firefox": {
-            "version_added": "22"
+            "version_added": "22",
+            "notes": [
+              "When pasting multiple files, only returns the first file. See [bug 1954680](https://bugzil.la/1954680).",
+              "Before Firefox 140, when pasting multiple files, and the first file was not acceptable, returned no file. See [bug 1961170](https://bugzil.la/1961170)."
+            ]
           },
           "firefox_android": "mirror",
           "ie": {