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user.js
Firefox privacy, security and anti-tracking: a comprehensive user.js template for configuration and hardening
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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
uBlockOrigin for sure is the only thing that you really need. Pay attention to Firefox settings (you can follow the Arkenfox guide or other guides like this one). Other useful privacy-related addons that I like are: PrivacyRedirect / LibRedirect and I don't care about cookies (this one is more about convenience)
I don't know if I'd go this far. You probably don't need an antivirus as much as you do on Windows. However, some cross-platform viruses can affect Linux (e.g. malicious browser extensions, Java viruses, infected Windows files run through Wine). It can also be useful for detecting Windows viruses in files which is still useful to know about if you're sharing files. And Linux viruses, while much less common, do exist. ClamAV is a good choice for a Linux antivirus.