We will use the last js value from arkenfox and this will automatically install ublock origin at launch (like librewolf)

// IMPORTANT: Start your code on the 2nd line
pref("_user.js.parrot", "START: Oh yes, the Norwegian Blue... what's wrong with it?");
pref("browser.aboutConfig.showWarning", false);
pref("_user.js.parrot", "0100 syntax error: the parrot's dead!");
pref("browser.startup.page", 0);
pref("browser.startup.homepage", "chrome://browser/content/blanktab.html");
pref("browser.newtabpage.enabled", false);
pref("browser.newtabpage.activity-stream.showSponsored", false);
pref("browser.newtabpage.activity-stream.showSponsoredTopSites", false);
pref("browser.newtabpage.activity-stream.showSponsoredCheckboxes", false);
pref("browser.newtabpage.activity-stream.default.sites", "");
pref("_user.js.parrot", "0200 syntax error: the parrot's definitely deceased!");
pref("geo.provider.ms-windows-location", false);
pref("geo.provider.use_corelocation", false);
pref("geo.provider.use_geoclue", false);
pref("_user.js.parrot", "0300 syntax error: the parrot's not pinin' for the fjords!");
pref("extensions.getAddons.showPane", false);
pref("extensions.htmlaboutaddons.recommendations.enabled", false);
pref("browser.discovery.enabled", false);
pref("browser.newtabpage.activity-stream.feeds.telemetry", false);
pref("browser.newtabpage.activity-stream.telemetry", false);
pref("app.shield.optoutstudies.enabled", false);
pref("app.normandy.enabled", false);
pref("app.normandy.api_url", "");
pref("breakpad.reportURL", "");
pref("browser.tabs.crashReporting.sendReport", false);
pref("browser.crashReports.unsubmittedCheck.autoSubmit2", false);
pref("captivedetect.canonicalURL", "");
pref("network.captive-portal-service.enabled", false);
pref("network.connectivity-service.enabled", false);
pref("_user.js.parrot", "0400 syntax error: the parrot's passed on!");
pref("browser.safebrowsing.downloads.remote.enabled", false);
pref("_user.js.parrot", "0600 syntax error: the parrot's no more!");
pref("network.prefetch-next", false);
pref("network.dns.disablePrefetch", true);
pref("network.dns.disablePrefetchFromHTTPS", true);
pref("network.predictor.enabled", false);
pref("network.predictor.enable-prefetch", false);
pref("network.http.speculative-parallel-limit", 0);
pref("browser.places.speculativeConnect.enabled", false);
pref("_user.js.parrot", "0700 syntax error: the parrot's given up the ghost!");
pref("network.proxy.socks_remote_dns", true);
pref("network.file.disable_unc_paths", true);
pref("network.gio.supported-protocols", "");
pref("_user.js.parrot", "0800 syntax error: the parrot's ceased to be!");
pref("browser.urlbar.speculativeConnect.enabled", false);
pref("browser.urlbar.quicksuggest.enabled", false);
pref("browser.urlbar.suggest.quicksuggest.nonsponsored", false);
pref("browser.urlbar.suggest.quicksuggest.sponsored", false);
pref("browser.search.suggest.enabled", false);
pref("browser.urlbar.suggest.searches", false);
pref("browser.urlbar.trending.featureGate", false);
pref("browser.urlbar.addons.featureGate", false);
pref("browser.urlbar.amp.featureGate", false);
pref("browser.urlbar.fakespot.featureGate", false);
pref("browser.urlbar.mdn.featureGate", false);
pref("browser.urlbar.weather.featureGate", false);
pref("browser.urlbar.wikipedia.featureGate", false);
pref("browser.urlbar.yelp.featureGate", false);
pref("browser.formfill.enable", false);
pref("browser.search.separatePrivateDefault", true);
pref("browser.search.separatePrivateDefault.ui.enabled", true);
pref("_user.js.parrot", "0900 syntax error: the parrot's expired!");
pref("signon.autofillForms", false);
pref("signon.formlessCapture.enabled", false);
pref("network.auth.subresource-http-auth-allow", 1);
pref("_user.js.parrot", "1000 syntax error: the parrot's gone to meet 'is maker!");
pref("browser.cache.disk.enable", false);
pref("browser.privatebrowsing.forceMediaMemoryCache", true);
pref("media.memory_cache_max_size", 65536);
pref("browser.sessionstore.privacy_level", 2);
pref("toolkit.winRegisterApplicationRestart", false);
pref("browser.shell.shortcutFavicons", false);
pref("_user.js.parrot", "1200 syntax error: the parrot's a stiff!");
pref("security.ssl.require_safe_negotiation", true);
pref("security.tls.enable_0rtt_data", false);
pref("security.OCSP.enabled", 1);
pref("security.OCSP.require", true);
pref("security.cert_pinning.enforcement_level", 2);
pref("security.remote_settings.crlite_filters.enabled", true);
pref("security.pki.crlite_mode", 2);
pref("dom.security.https_only_mode", true);
pref("dom.security.https_only_mode_send_http_background_request", false);
pref("security.ssl.treat_unsafe_negotiation_as_broken", true);
pref("browser.xul.error_pages.expert_bad_cert", true);
pref("_user.js.parrot", "1600 syntax error: the parrot rests in peace!");
pref("network.http.referer.XOriginTrimmingPolicy", 2);
pref("_user.js.parrot", "1700 syntax error: the parrot's bit the dust!");
pref("privacy.userContext.enabled", true);
pref("privacy.userContext.ui.enabled", true);
pref("_user.js.parrot", "2000 syntax error: the parrot's snuffed it!");
pref("media.peerconnection.ice.proxy_only_if_behind_proxy", true);
pref("media.peerconnection.ice.default_address_only", true);
pref("_user.js.parrot", "2400 syntax error: the parrot's kicked the bucket!");
pref("dom.disable_window_move_resize", true);
pref("_user.js.parrot", "2600 syntax error: the parrot's run down the curtain!");
pref("browser.download.start_downloads_in_tmp_dir", true);
pref("browser.helperApps.deleteTempFileOnExit", true);
pref("browser.uitour.enabled", false);
pref("devtools.debugger.remote-enabled", false);
pref("permissions.manager.defaultsUrl", "");
pref("network.IDN_show_punycode", true);
pref("pdfjs.disabled", false);
pref("pdfjs.enableScripting", false);
pref("browser.tabs.searchclipboardfor.middleclick", false);
pref("browser.contentanalysis.enabled", false);
pref("browser.contentanalysis.default_result", 0);
pref("security.csp.reporting.enabled", false);
pref("browser.download.useDownloadDir", false);
pref("browser.download.alwaysOpenPanel", false);
pref("browser.download.manager.addToRecentDocs", false);
pref("browser.download.always_ask_before_handling_new_types", true);
pref("extensions.enabledScopes", 5);
pref("extensions.postDownloadThirdPartyPrompt", false);
pref("_user.js.parrot", "2700 syntax error: the parrot's joined the bleedin' choir invisible!");
pref("browser.contentblocking.category", "strict");
pref("_user.js.parrot", "2800 syntax error: the parrot's bleedin' demised!");
pref("privacy.sanitize.sanitizeOnShutdown", true);
pref("privacy.clearOnShutdown_v2.cache", true);
pref("privacy.clearOnShutdown_v2.historyFormDataAndDownloads", false);
pref("privacy.clearOnShutdown_v2.browsingHistoryAndDownloads", false);
pref("privacy.clearOnShutdown_v2.downloads", false);
pref("privacy.clearOnShutdown_v2.formdata", true);
pref("privacy.clearOnShutdown_v2.cookiesAndStorage", true);
pref("privacy.clearSiteData.cache", true);
pref("privacy.clearSiteData.cookiesAndStorage", false);
pref("privacy.clearSiteData.historyFormDataAndDownloads", false);
pref("privacy.clearSiteData.browsingHistoryAndDownloads", false);
pref("privacy.clearSiteData.formdata", true);
pref("privacy.clearHistory.cache", true);
pref("privacy.clearHistory.cookiesAndStorage", false);
pref("privacy.clearHistory.historyFormDataAndDownloads", false);
pref("privacy.clearHistory.browsingHistoryAndDownloads", false);
pref("privacy.clearHistory.formdata", true);
pref("privacy.sanitize.timeSpan", 0);
pref("_user.js.parrot", "4000 syntax error: the parrot's bereft of life!");
pref("_user.js.parrot", "4500 syntax error: the parrot's popped 'is clogs");
pref("privacy.window.maxInnerWidth", 1600);
pref("privacy.window.maxInnerHeight", 900);
pref("privacy.resistFingerprinting.block_mozAddonManager", true);
pref("privacy.spoof_english", 1);
pref("widget.non-native-theme.use-theme-accent", false);
pref("browser.link.open_newwindow", 3);
pref("browser.link.open_newwindow.restriction", 0);
pref("_user.js.parrot", "5000 syntax error: the parrot's taken 'is last bow");
pref("_user.js.parrot", "5500 syntax error: this is an ex-parrot!");
pref("_user.js.parrot", "6000 syntax error: the parrot's 'istory!");
pref("extensions.blocklist.enabled", true);
pref("network.http.referer.spoofSource", false);
pref("security.dialog_enable_delay", 1000);
pref("privacy.firstparty.isolate", false);
pref("extensions.webcompat.enable_shims", true);
pref("security.tls.version.enable-deprecated", false);
pref("extensions.webcompat-reporter.enabled", false);
pref("extensions.quarantinedDomains.enabled", true);
pref("_user.js.parrot", "7000 syntax error: the parrot's pushing up daisies!");
pref("_user.js.parrot", "8000 syntax error: the parrot's crossed the Jordan");
pref("_user.js.parrot", "8500 syntax error: the parrot's off the twig!");
pref("datareporting.policy.dataSubmissionEnabled", false);
pref("datareporting.healthreport.uploadEnabled", false);
pref("toolkit.telemetry.unified", false);
pref("toolkit.telemetry.enabled", false);
pref("toolkit.telemetry.server", "data:,");
pref("toolkit.telemetry.archive.enabled", false);
pref("toolkit.telemetry.newProfilePing.enabled", false);
pref("toolkit.telemetry.shutdownPingSender.enabled", false);
pref("toolkit.telemetry.updatePing.enabled", false);
pref("toolkit.telemetry.bhrPing.enabled", false);
pref("toolkit.telemetry.firstShutdownPing.enabled", false);
pref("toolkit.telemetry.coverage.opt-out", true);
pref("toolkit.coverage.opt-out", true);
pref("toolkit.coverage.endpoint.base", "");
pref("_user.js.parrot", "9000 syntax error: the parrot's cashed in 'is chips!");
pref("browser.startup.homepage_override.mstone", "ignore");
pref("browser.newtabpage.activity-stream.asrouter.userprefs.cfr.addons", false);
pref("browser.newtabpage.activity-stream.asrouter.userprefs.cfr.features", false);
pref("browser.urlbar.showSearchTerms.enabled", false);
pref("_user.js.parrot", "9999 syntax error: the parrot's shuffled off 'is mortal coil!");
pref("browser.shopping.experience2023.enabled", false);
pref("browser.urlbar.pocket.featureGate", false);
pref("_user.js.parrot", "SUCCESS: No no he's not dead, he's, he's restin'!");

This is the content of user.js from arkenfox (140.1) it might change in the future so don't rely on this guide for the next version of arkenfox.

There is a python3 script available to convert the whole content of the user.js from arkenfox in a firefox.cfg with the correct syntax.

#!/usr/bin/env python3
"""
Convert lines like:
  user_pref("privacy.clearOnShutdown_v2.cookiesAndStorage", true);
to an autoconfig firefox.cfg containing pref(...) lines.

Usage:
  python3 .py [input_file]
If no input_file given, reads stdin.
"""

import sys
import re
from pathlib import Path

USER_PREF_RE = re.compile(
    r'^\s*(?P<prefix>//\s*)?user_pref\(\s*"(?P<name>[^"]+)"\s*,\s*(?P<value>.+?)\s*\)\s*;\s*(?://.*)?$'
)

def normalize_value(val_str):
    v = val_str.strip()
    # Keep strings quoted, booleans and numbers unquoted, arrays/objects unchanged
    if (v.startswith('"') and v.endswith('"')) or (v.startswith("'") and v.endswith("'")):
        return v
    if v.lower() in ("true", "false"):
        return v.lower()
    # Try numeric
    try:
        float(v)
        return v
    except Exception:
        pass
    # Fallback: ensure it's a JS string
    escaped = v.replace('"', '\\"')
    return f'"{escaped}"'

def process_lines(lines):
    out_lines = []
    for ln in lines:
        m = USER_PREF_RE.match(ln)
        if not m:
            continue
        # If the line is commented (prefix captured) skip
        if m.group('prefix'):
            continue
        name = m.group('name')
        raw_value = m.group('value')
        # If the value itself is commented out (e.g. // at start) skip
        if raw_value.strip().startswith("//"):
            continue
        value = normalize_value(raw_value)
        out_lines.append(f'pref("{name}", {value});')
    return out_lines

def main():
    # Read input
    if len(sys.argv) > 1:
        p = Path(sys.argv[1])
        if not p.exists():
            print(f"Input file not found: {p}", file=sys.stderr)
            sys.exit(2)
        src = p.read_text(encoding='utf-8').splitlines()
    else:
        src = sys.stdin.read().splitlines()

    prefs = process_lines(src)

    if not prefs:
        print("No user_pref(...) lines found.", file=sys.stderr)
        sys.exit(1)

    out_path = Path("firefox.cfg")
    header = "// IMPORTANT: Start your code on the 2nd line\n"
    content = header + "\n".join(prefs) + "\n"
    out_path.write_text(content, encoding='utf-8', newline="\n")
    print(f"Wrote {len(prefs)} prefs to {out_path}")

if __name__ == "__main__":
    main()

python3 p.py user.js

This will create a file called "firefox.cfg" and if you open the file you will see the whole content of arkenfox user.js.

sudo mv firefox.cfg /usr/lib/firefox/

Done ! Every time you will start your DispVM or AppVM it will start with the arkenfox pref and install ublock origin automatically now

You will have to change in the future the ublock origin version in the policies.json file we created to use the last version in the future.

I edited the post because i realize that using the arkenfox pref inside policies.json was a bad idea because some telemetry was still enable even with the pref value from arkenfox. By looking at the mozilla doc i see we could use autoconfig instead to do this. By the way i have a error saying "New user can only use 2 links in a post" so i removed some link in the post.

Edit : I forget to give the content of /etc/firefox/policies/policies.json i updated the post

Set firefox arkenfox preferences in template