Why can I specify some preferences in policies.json, but not others?

[honreir]

I'm trying to pre-configure Firefox for all users using policies.json. I'm currently able to set preferences like this:

{
    "policies": {
        "Preferences": {
            "browser.toolbars.bookmarks.visibility": "never",
            ...
        }
}

This works well for the most part, but some preferences don't seem to be able to be set this way. Namely, I'm trying to set full-screen-api.ignore-widgets to true, but it doesn't seem to work. I am able to set it via about:config or a user.js file, but would prefer to set it in policies.json if possible. Why doesn't this work the way I am expecting?

[mkaply]

We don't allow all preferences to be set because we were trying to avoid people messing with settings that they didn't fully understand that could impact the browser negatively.

I've never had a request for any full-screen-api preferences until now :)

What's the reason for setting this pref (just curious)

I can look at adding them

[honreir]

For the full-screen-api.ignore-widgets option specifically, enabling it allows me to have a windowed full screen experience. I am using a tiling window manager, and this way I can treat Firefox like any other window, while still being in "full screen" mode, ie no tab/address bars.

I am going through many of the preferences partially to tailor the browser to my system/needs, but also just to learn about the available options. The environment I'm setting up launches a fresh unused containerized environment for each session (not browser session necessarily, more like workflow sessions). These sessions could be persistent, but also often are newly created. The Firefox profile directory isn't created until the first launch, thus my need for a global configuration.

I found some other options that aren't configurable in policies.json too, such as many of the toolkit.telemetry. options. I would be happy with a user.js style global configuration instead if I could get that working. I tried creating an /etc/firefox/defaults/pref/autoconfig.js file that sets general.config.filename to a custom config file (found in /etc/firefox/config.cfg), but wasn't able to get that to work either.

I appreciate the help.

[celenityy]

I tried creating an /etc/firefox/defaults/pref/autoconfig.js file that sets general.config.filename to a custom config file (found in /etc/firefox/config.cfg), but wasn't able to get that to work either.

I've been meaning to file a bug for this; I'm fairly certain that using a .cfg file at /etc/firefox on Linux was never implemented (I've at least never been able to make it work either...).

Putting the .cfg file at /usr/lib/firefox (or /usr/lib64/firefox, depending on your distro) should work for you for the time being.

[honreir]

Awesome, that works! While I wouldn't want to pollute /usr on my main machine, this works fine for what I'm doing.