vscode.dev: Markdown Editor doesn't render & Markdown Preview renders very slowly

Does this issue occur when all extensions are disabled?: Yes

- VS Code Version: 1.135.0 (https://vscode.dev - web version of VS Code, NOT local install)
- Run in Browser: Firefox 154.0.1 (on Ubuntu 26.04)

Steps to Reproduce:

1. In https://vscode.dev (web version of VS Code), open a markdown file.
2. By default it opens in Text Editor mode. Switch to Markdown Preview mode by clicking on the dropdown menu at top right of the markdown document tab. This renders very slowly (tab remains blank for a few minutes and then renders).
3. Switch to Markdown Editor mode. Now it remains blank only, doesn't render at all!