How to enter "work offline" mode in firefox kiosk mode using keyboard shortcut?

[szymucha94]

I got couple of tablets running linux and firefox in kiosk mode, displaying frontend that consumes a lot of resources due to gigantic amount of events coming through. FE implementation is beyond my control.
Because these tablets got their screens turned off almost all the time, in order to save CPU and flash-based disks, I'm suspending the firefox process and resuming it when it's required. Problem is that un-suspending process makes it lag a lot because of processing all pending events. This takes A LOT of time which is unacceptable.

So, to the point: I found a way to interrupt the event-listener by going into offline mode, then going out of it after unpausing process. In normal firefox. In kiosk mode there is no "file" button to press, nor "application menu". And I need to do it automatically, preferably via simulating keypresses. AFAIK there is no shortcut to go offline by default.
Is there any solution to this? I'd rather continue using firefox instead of switching to chrome.

[mkaply]

Can you simulate navigating the menu?

There is no keystroke for this

[szymucha94]

How can I simulate navigating the menu when there is no menu in kiosk mode?

[mkaply]

For some reason I thought the menu was just offscreen, but you're right, it doesn't work.

I can't think of a good way to do what you're asking. You can start Firefox offline with a "-offline" parameter, but that parameter doesn't work if Firefox has already been started.

[mkaply]

For some reason I thought the menu was just offscreen, but you're right, it doesn't work.

I can't think of a good way to do what you're asking. You can start Firefox offline with a "-offline" parameter, but that parameter doesn't work if Firefox has already been started.

[szymucha94]

I might be able to build something simple for you.

I'm confused though. Are you using the Snap?

I'm using snap image of firefox, version 3216 (118.0.1), build id 20230929164800. Unfortunately standalone firefox can no longer be installed on ubuntu.

[mkaply]

I've built some simple code that will make this work on your build.

It uses autoconfig.

You'll want to check this bug:

https://bugzilla.mozilla.org/show_bug.cgi?id=1785278

So basically you put this in a file called offline_key.cfg in /etc/firefox

// Autoconfig file created by Mike Kaply
const {classes: Cc, interfaces: Ci, utils: Cu} = Components;

try {
  Cu.import("resource://gre/modules/Services.jsm");
} catch (e) {

}

var observer = {
  observe: function observe(subject, topic, data) {
    switch (topic) {
      case "chrome-document-global-created":
        let win = subject;
        win.addEventListener("load", function onLoad(event) {
          win.removeEventListener("load", onLoad, false);
          let doc = event.target;
          let url = doc.location.href.split("?")[0].split("#")[0];
          switch (url) {
            case "chrome://browser/content/browser.xhtml":
              let keyset = doc.getElementById("mainKeyset");
              let key = doc.createElementNS("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul", "key");
              key.setAttribute("keycode", "VK_F12");
              key.setAttribute("command", "cmd_toggleOfflineStatus");
              keyset.appendChild(key);
              let goOffline = doc.getElementById("goOfflineMenuitem");
              goOffline.setAttribute("key", "toggleOfflineStatus")
              break;
          }
        }, false);
        break;
    }
  }
}

Services.obs.addObserver(observer, "chrome-document-global-created", false);

Then you create a file in /etc/firefox/defaults called offline_key.js and you put in it:

pref("general.config.filename", "offline_key.cfg");
pref("general.config.obscure_value", 0);
pref("general.config.sandbox_enabled", false);

Once you do this, F12 will do offline/online

[mkaply]

I didn't test Snap specifically, but based on what I know, this should work (I'm pretty sure we made Autoconfig work in Snap)

[mkaply]

Also, this part is unnecessary

              let goOffline = doc.getElementById("goOfflineMenuitem");
              goOffline.setAttribute("key", "toggleOfflineStatus")

We're just adding the key.

[szymucha94]

It works, but with minor change: key that works is F10 (F12 opens dev console instead) and I had to place offline_key.js into /etc/firefox/defaults/pref/
Thank you!

[mkaply]

Awesome, glad we got it figured out.