Linux: Right-click → Copy does not copy selected text when widget.gtk.native-context-menus is enabled

### Preliminary Checks - [x] I have read and understood the important section above. - [x] I have searched existing issues and avoided creating duplicates. - [x] I am not filing an enhancement request. - [x] I have checked that this issue cannot be reproduced on Mozilla Firefox. - [x] I have checked that this issue can be reproduced once I removed all my Mods and Custom CSS. ### What happened? ## What happened? On Linux, copying selected text via the web page context menu does not work when the Firefox preference widget.gtk.native-context-menus = true is enabled. The context menu opens normally, the "Copy" item is present and can be clicked, but nothing is placed into the clipboard. Keyboard copying with Ctrl+C works correctly, and middle-click/paste also works correctly. ## Expected behavior Right-clicking selected text and choosing "Copy" should copy the selected text to the clipboard. ## Steps to reproduce 1. Run Zen on Linux. 2. Select some text on a web page. 3. Right-click the selection. 4. Click "Copy". 5. Paste the clipboard contents somewhere else. Actual result: Nothing is copied. ## Workaround Set the following preference to false: widget.gtk.native-context-menus = false After restarting Zen, right-click → Copy works correctly. ## Environment - Zen: 1.21.14b - Firefox: 153.0.4 (64-bit) - OS: openSUSE Tumbleweed - Desktop: KDE Plasma - Session: Wayland - Also reproduced under X11 ## Additional testing - Ctrl+C works. - Middle mouse button paste works. - The context menu itself remains open and behaves normally. - Firefox 153.0.3 (64-bit) on the same system does NOT have this problem. - Zen Troubleshoot Mode does not fix the problem. - Disabling extensions does not fix the problem. - A new/clean Zen profile does NOT have the problem. - The problem occurs with the existing Zen profile. - Setting `widget.clipboard.use-cached-data.enabled = false` does not fix the problem. - Resetting `dom.events.testing.asyncClipboard` does not fix the problem. The problem is reproducible simply by enabling: widget.gtk.native-context-menus = true and disappears when setting it to: widget.gtk.native-context-menus = false ### Expected behavior Linux: Right-click → Copy does not copy selected text when widget.gtk.native-context-menus is enabled ### Actual behavior Linux: Right-click → Copy does not copy selected text when widget.gtk.native-context-menus is enabled ### Steps to reproduce 1. Open Zen Browser on Linux. 2. Open about:config. 3. Set widget.gtk.native-context-menus to true. 4. Restart Zen Browser. 5. Open any web page containing selectable text. 6. Select some text. 7. Right-click the selected text. 8. Select Copy from the context menu. 9. Paste the clipboard contents into another application, e.g. Kate. 10. Observe that nothing was copied. Expected: The selected text is copied to the clipboard. Actual: The context menu works normally and Copy can be clicked, but the selected text is not copied. Workaround: Set widget.gtk.native-context-menus to false and restart Zen. Right-click → Copy then works normally. ### Screenshots and videos _No response_ ### Version 1.21.14b (Firefox 153.0.4) (64-Bit) ### What platform are you seeing the problem on? Linux (Tarball) ### What component is this issue related to? Performance ### Relevant log output if applicable ```shell ```