I love Firefox because with about:config and User css you can configure it just like you want it. Also Falkon because you get a fully featured browser that runs decently on older hardware
The short answer: NetSurf, because it is the only contemporary web browser that also works under Plan 9, is extremely resource-efficient and is not based on one of the big (= commercial) browser engines.
The long answer: It depends. I like to use eww to test the accessibility of a website, but since Mozilla destroyed everything I liked about Firefox in November 2017, I’ve been using Vivaldi as my main browser. Although Vivaldi is based on Chromium, it is quite privacy-friendly, performant and extremely customisable. Unfortunately, some websites do not work very well with NetSurf. (I like to report this as a bug to the website operator. It is fatal that everyone always assumes that everyone wants to load and execute hundreds of KiB of JavaScript).
Why would your trust in Mozilla have anything to do with using this browser? Do you trust google more than Mozilla or why would you use a chromium based browser instead?
Why would your trust in Mozilla have anything to do with using this browser?
Browsers based on Firefox are at the mercy of Mozilla. If Mozilla once again delivers a new function that is directed against privacy, those who develop Firefox-based browsers must either deactivate this function or also deliver it. And this is not always clearly documented. And Mozilla has simply acted against my interests too often - I no longer even trust LibreWolf.
(Leaving this aside, I also fail to see any advantage of Zen over Vivaldi.)
Same thing can be said about Vivaldi, which is based on chromium (Google). Also like you said they (librewolf, zen) can disable privacy invasive features, what they do, just like chromium based browsers do (or do not) remove google tracking
Zen is open source and has no tracking by default compared to Vivaldi and will continue to support the web request api
I know that this might be an unpopular opinion, but I don’t really care about whether the software I use every day is open source or not, given that I rarely need to look into the source code anyway. (Do you?) Is the webRequest API about to be phased out?
I don’t check the source code of something big browsers, that’s a little beyond my understanding, but that’s why there are experts for that.
The webrequest api (or rather the main parts) have already been phased out of chromium, so it’s just a matter of time until Vivaldi rebases to the newest version and gets rid of the api. (I think they said they want to delay the depreciation but acknowledged that it is inevitably coming, probably sooner than later)
Upvoted for NetSurf. I wrote the Amiga frontend for it, and as such it’s my favourite browser on that platform (OS4 anyway - the OS3 build is very unstable)
Sadly not available on Linux, but Arc has the best tab management paradigm of any browser I’ve tried, by far. Pinned tabs with folders, workspaces, and home urls goes hard.
On the other end of the spectrum, I’m very fond of qtbrowser. If you want a keyboard centered workflow it’s hard to beat.