I didn't get very far into exploring their options/services/addons, and I don't want to spam you with a bunch of questions on here, but do those both have browser extension options? Mullvad was advertising an entirely separate browser.
I just don't really have a lot of VPN experience and many people on things I've looked up since this talk about security issues from free VPNs, even Proton, so I guess I'm just being cautious and wanting to be sure of things.
No worries, I'll try to answer to the best of my knowledge.
Yes, both
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and
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have browser extensions, although the Mullvad extension is only available on Firefox whereas Proton has it available on both Firefox and chromium browsers (Chrome, Brave, Internet Explorer, etc.). The Mullvad web browser is optional. If you're just browsing and downloading, then the extension/add-on is really all you're going to need.
If it's security you're worried about, there's never going to be 100% anonymity with these things. But you can take a bit of solace in knowing that both services have a no logs policy (your information and data won't be recorded) if you pay for a subscription. They're also open source which is good, if anything nefarious were going on, the community would've been able to call it out a long time ago.
Now free vpns aren't entirely user friendly. Even though they are free, there will always be a cost. It may be limited access to their services like putting time limits when you connect to one of their servers, access to only a select few countries, or even selling your data which is a common one since it's a way for them profit while being free. Proton's free plan contains some of these limitations which is why you hear complaints about it. Free vpn = bad usually.
You can't go wrong with either option for what you are doing but if you want my suggestion, get a Proton subscription. It's just better for general use.