Website lateral menu doesn't load without javaScript

Visiting https://forge.rust-lang.org/ with JavaScript disabled does not load the lateral menu. <details><summary>Screenshot</summary> <p> <img alt="Image" src="https://github.com/user-attachments/assets/e2420cd6-626e-4426-9e37-1bdd2f8e99c0" /> </p> </details> The error page in the screenshot leads to this Mozilla support page: https://support.mozilla.org/en-US/kb/xframe-neterror-page Trying to understand where the issue is, I did some tests: - I can reproduce this also on Firefox Linux stable (141.0.3), fresh install and no other extension than the one to disable JS - I've tried building the website and serving from localhost:3000 and I can't reproduce, the menu works just fine without JavaScript. I've built with mdbook 0.4.51 and 0.4.52 - The [rustc-dev website](https://rustc-dev-guide.rust-lang.org) does not show this behaviour (works just fine without JavaScript) I can't say a lot more because I am not familiar with the deploying of this website so I'm not sure I can pin this issue on MDBook or on the website code. Any idea where the problem could be? thanks