Those Nextcloud links allow me to download the files, but I don't think they open the same editor view you are seeing. There is not place for Firenvim to be involved from an end users view without an account on your server (or a federated instance).

Hmm I tested it several times, you should be able to edit the links files exposed by those links. @glacambre tested it, too.

What browser are you using?

Firefox on Linux here. It's not presenting me much besides a download link. I even tried the "add to your Nextcloud", but it doesn't let me enter the address of my own Nextcloud instance and I assume it's limited to a federation whitelist of some sort.

@alerque Very weird, I can access the documents, served under a prosemirror instance, and edit them in Firenvim with the dedicated browser shortcut.

Maybe your Firefox is too old or one of your extension is interfering?

No my Firefox is not too old and I checked extensions. Yes I did find the trouble. Firefox has a crazy pants way of (not) recovering from a few errors. At the time I first opened something on that domain the disk where my cache was was full. Firefox noted the error, but now even having cleared up 100+ Gigs on the cache disk, rebooted, restarted Firefox, and trying to refresh the site it keeps throwing an NS_ERROR_FILE_NO_DEVICE_SPACE error silently in the background.

This is not the site, Nextcloud, Firenvim, or any extension's fault: it is a known bug in Firefox that it doesn't recover from this error gracefully. I've run into it before on other sites and I think you have to manually clear local storage or something for the site to get it to recover. For the life of me I can't figure out what the magic sequence is right now. It works fine in private browsing mode but even with all extensions disabled and "clear site data and cookies" it still won't run in normal mode for me.

Relevant Firefox bug report (opened 7 years ago).