Both Firefox and Chromium has support for what is sometimes called webworkers.
These workers uses websocket and runs in the background unless you deliberately disable the functionality.
These are usually legit - that is if one doesn’t exhibit extremely lazy or outright dangerous browsing habits. Not so long ago I only had a shrug for those saying javascript whas dangerous - I was ignorant - javascript can be used to start websockets and thus scan your system for vulnerabililties and try to exploit them.
I am by no means saying this is the case - just venting the possibility.
With your last edit - while something could appear legit - others raise eyebrows - such as censys.io
- note - I am not saying there isn’t a legit reason for hiding - it could be they don’t want to expose the employee which registered the domain on behalf of the company - nonetheless - initially it raises my eyebrows
$ whois censys.io
Domain Name: censys.io
Registry Domain ID: 66224c6b278243f1ab3261f34df5c7c4-DONUTS
Registrar WHOIS Server: key-systems.net
Registrar URL: http://key-systems.net
Updated Date: 2021-06-21T15:33:21Z
Creation Date: 2015-08-13T19:50:44Z
Registry Expiry Date: 2026-08-13T19:50:44Z
Registrar: Key-Systems GmbH
Registrar IANA ID: 269
Registrar Abuse Contact Email: abuse@key-systems.net
Registrar Abuse Contact Phone: +49 6894 9396 850
Domain Status: clientTransferProhibited https://icann.org/epp#clientTransferProhibited
Registry Registrant ID: REDACTED FOR PRIVACY
Registrant Name: REDACTED FOR PRIVACY
Registrant Organization: c/o whoisproxy.com
Registrant Street: REDACTED FOR PRIVACY
Registrant City: REDACTED FOR PRIVACY
Registrant State/Province: VA
Registrant Postal Code: REDACTED FOR PRIVACY
Registrant Country: US
Registrant Phone: REDACTED FOR PRIVACY
Registrant Phone Ext: REDACTED FOR PRIVACY
Registrant Fax: REDACTED FOR PRIVACY
Registrant Fax Ext: REDACTED FOR PRIVACY
Registrant Email: Please query the RDDS service of the Registrar of Record identified in this output for information on how to contact the Registrant, Admin, or Tech contact of the queried domain name.
Registry Admin ID: REDACTED FOR PRIVACY
Admin Name: REDACTED FOR PRIVACY
Admin Organization: REDACTED FOR PRIVACY
Admin Street: REDACTED FOR PRIVACY
Admin City: REDACTED FOR PRIVACY
Admin State/Province: REDACTED FOR PRIVACY
Admin Postal Code: REDACTED FOR PRIVACY
Admin Country: REDACTED FOR PRIVACY
Admin Phone: REDACTED FOR PRIVACY
Admin Phone Ext: REDACTED FOR PRIVACY
Admin Fax: REDACTED FOR PRIVACY
Admin Fax Ext: REDACTED FOR PRIVACY
Admin Email: Please query the RDDS service of the Registrar of Record identified in this output for information on how to contact the Registrant, Admin, or Tech contact of the queried domain name.
Registry Tech ID: REDACTED FOR PRIVACY
Tech Name: REDACTED FOR PRIVACY
Tech Organization: REDACTED FOR PRIVACY
Tech Street: REDACTED FOR PRIVACY
Tech City: REDACTED FOR PRIVACY
Tech State/Province: REDACTED FOR PRIVACY
Tech Postal Code: REDACTED FOR PRIVACY
Tech Country: REDACTED FOR PRIVACY
Tech Phone: REDACTED FOR PRIVACY
Tech Phone Ext: REDACTED FOR PRIVACY
Tech Fax: REDACTED FOR PRIVACY
Tech Fax Ext: REDACTED FOR PRIVACY
Tech Email: Please query the RDDS service of the Registrar of Record identified in this output for information on how to contact the Registrant, Admin, or Tech contact of the queried domain name.
Name Server: arturo.ns.cloudflare.com
Name Server: anastasia.ns.cloudflare.com
DNSSEC: unsigned
URL of the ICANN Whois Inaccuracy Complaint Form: https://www.icann.org/wicf/
>>> Last update of WHOIS database: 2022-04-29T13:12:20Z <<<
For more information on Whois status codes, please visit https://icann.org/epp
Terms of Use: Donuts Inc. provides this Whois service for information purposes, and to assist persons in obtaining information about or related to a domain name registration record. Donuts does not guarantee its accuracy. Users accessing the Donuts Whois service agree to use the data only for lawful purposes, and under no circumstances may this data be used to: a) allow, enable, or otherwise support the transmission by e-mail, telephone, or facsimile of mass unsolicited, commercial advertising or solicitations to entities other than the registrar's own existing customers and b) enable high volume, automated, electronic processes that send queries or data to the systems of Donuts or any ICANN-accredited registrar, except as reasonably necessary to register domain names or modify existing registrations. When using the Donuts Whois service, please consider the following: The Whois service is not a replacement for standard EPP commands to the SRS service. Whois is not considered authoritative for registered domain objects. The Whois service may be scheduled for downtime during production or OT&E maintenance periods. Queries to the Whois services are throttled. If too many queries are received from a single IP address within a specified time, the service will begin to reject further queries for a period of time to prevent disruption of Whois service access. Abuse of the Whois system through data mining is mitigated by detecting and limiting bulk query access from single sources. Where applicable, the presence of a [Non-Public Data] tag indicates that such data is not made publicly available due to applicable data privacy laws or requirements. Should you wish to contact the registrant, please refer to the Whois records available through the registrar URL listed above. Access to non-public data may be provided, upon request, where it can be reasonably confirmed that the requester holds a specific legitimate interest and a proper legal basis for accessing the withheld data
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It could be as simple as a service used by an adblocker or a malware scanner.
Remember that both Firefox and Chromium has settings which enables lookups in databases for malware domains - to prevent the casual user from accidently browse such bad places.
censys.io
is registered in 2015 - malware domains or domains connected to shady activity usually don’t last that long
A lot of possibilities exist to explain the traffic.
Without knowing anything - the members of this forum litereally doesn’t know anything - of what is going on your system.
It depend on the services you use - the applications you have installed - e.g. snap, flatpak, appimage - custom PKGBUILD from AUR - Electron based applications (yes they are webbrowser subsets) usually based on Chromium.
The list of recently visited websites - the dashboard of a browser - they all initiale a request when you open the browser.
Firefox defaults to send telemetry unless you actively disable it - try browsing this in firefox about:preferences#privacy