Are Chrome extensions compatible with Firefox?

For example I just tried the linked userscript for [Modern Hacker News](https://chromewebstore.google.com/detail/modern-for-hacker-news/dabkegjlekdcmefifaolmdhnhdcplklo) in Firefox, and it seems to be broken. It's a site-specific extension, so from what I read in the about page it should work I guess?