What Sval keeps private

Sval sends no usage data, and contacts only the services named on this page. A test launches Sval on a fresh install, records every connection it makes, and fails on any host that isn’t on Sval’s list.

What stays on your computer

Sval doesn’t run a sync service. When you sync, your devices meet in a folder you choose, and everything Sval writes there is encrypted with your sync key. See How sync works.

Several protections that need outside data download the whole list and check it on your device:

Ad and tracker blocking. Sval downloads each filter list from the group that publishes it, and matches every request against the lists on your device.
Dangerous site warnings. Sval downloads Google Safe Browsing’s lists of phishing and malware sites, and checks addresses on your device. When an address matches, Sval sends Google a short fragment of a hash to confirm it, never the address itself.
Data breach warnings. Sval downloads Have I Been Pwned’s whole list of breaches from Mozilla, and matches the site you’re on against it on your device. When you turn breach warnings off, Sval doesn’t download the list.
Translation. Pages are translated on your device. Sval downloads the translation models it needs.

Cookies and site data stay on the device. Sval never syncs them.

Choices you make in a private window last until you close it, and never sync.

What Sval writes about itself

The log. Sval writes warnings and errors to sval-log.txt in its data folder. The log never includes a Workspace, group, or tab name, a URL, or a secret.
Crash reports. A crash report leaves your computer only when you check the box to send it. It goes to Sval’s feedback server, which stores no IP address and no identifier.
Feedback. Send Feedback sends a report only when you select Send.

What Sval contacts

Out of the box, Sval contacts these services, each for a reason:

Sval’s update server, once a day, to check for updates. The request reveals only your release channel and platform.
The publishers of your filter lists, to keep blocking up to date. A list you add is contacted the way a page you open is. A list added on another device downloads only once you allow it on this one.
Mozilla’s Remote Settings, checked every hour, for data that protects you: revoked certificates, blocked extensions and drivers, tracking protection data and the site fixes it needs, cookie banner rules, password rules, translation models, and the breach list. Each request carries your IP address and nothing about your browsing. Sval downloads nothing else from it.
addons.mozilla.org, to check for updates to your extensions. The check tells it which extensions you have installed.
Google Safe Browsing, under Sval’s own key, for the lists of dangerous sites.
Your search engine, for suggestions as you type. It sees what you type before you search. DuckDuckGo is the default. Settings › Search turns suggestions off, and private windows keep them off.
Cisco’s OpenH264 codec, once per release, so video calls work on sites that use H.264. Cisco has to distribute it for licensing reasons.
Mozilla’s Web Push service, only while a site you allowed can send you notifications.

Sval contacts these only once you choose them:

Kagi, when you choose Kagi as your search engine.
An encrypted DNS resolver, when you turn on Secure DNS. Sval contacts only the resolver you pick.
Google’s Widevine download, the first time a site needs it to play protected video and you agree.
addons.mozilla.org, when you install an extension or choose a password manager.
Sval’s feedback server, when you send feedback or a crash report.

Sval turns off contacts Firefox makes on its own. Among them are telemetry, studies, and experiments, Mozilla’s update and region checks, sponsored suggestions and weather, connection checks, the extension recommendations that send Mozilla your list of extensions, network location lookups, and Firefox accounts. Sval’s location comes from your operating system alone.

Against tracking

Sval blocks ads and trackers with open-source filter lists. A new install uses Balanced Blocking, which blocks what uBlock Origin blocks out of the box. Strict Blocking also blocks trackers in links, social widgets, and scam sites, and strips tracking parameters from the addresses you open.

Some sites load a tracker from an address on their own domain that points to the tracker’s servers. When blocking is on, Sval looks up where each such address leads and blocks it when it leads to a tracker. When you use a proxy, Sval skips this check, because looking up an address would reveal it outside the proxy.

Cookies start on Keep each site’s cookies to that site, so a company’s cookie on one site can’t follow you to another.

Global Privacy Control is on, telling sites not to sell or share your data. In some places the law requires them to honor it.

Against fingerprinting

Sites can tell browsers apart by reading details of the device, such as its screen, fonts, and graphics card. Sval’s fingerprinting protection gives sites values that make you look like other Sval users, and rarely breaks sites.

Protection runs in every window, so a private window doesn’t stand out from a normal one.
Sites see only your first language, unless you turn on Tell sites all your languages.
Each site sees its own count of processor cores, between half yours and all of them.
Sval doesn’t use the list Mozilla publishes that weakens protection on Google’s and Bing’s sites. You can turn it on in Settings.

Strict fingerprinting protection hides more, and breaks more sites. Any site’s protection can be turned off when it breaks the site.

What this doesn’t cover

Your network sees the sites you look up, unless you turn on Secure DNS.
Sites you sign in to know who you are. An isolated Workspace keeps a sign-in apart from your other Workspaces. See What an isolated Workspace keeps apart.