Sharing my experience here about the benefits of the Containers/First Party Isolate feature.
Before mid-2020 I kind of exclusively used Firefox since Firefox Quantum Nightly came out in 2017 I believe and have also used containers since it came out. I have social media accounts on most of the common and popular platforms like Facebook, Twitter, Instagram, Reddit but targeted ads are turned off on all platforms including Google. When I used Firefox I kind of never saw any targeted ads in apps like Facebook on Android. I also used Firefox on my Android phone BTW.
But ever since I started to try out Edge in mid-2020, I started to see targeted ads on Facebook and Twitter. It got really bad in 2021. I can't escape facebook's targeted ads ever since I started using Edge as my main browser on the PC as well as Android.
I purchased a 4k Android Smart TV two weeks ago so as we all do, I researched for a couple of weeks prior to that (google search) to decide which TV fits my needs and budget the most. Lo and behold, after a couple of days of searching I only and only saw Smart TV-related ads on Facebook. Sony, Samsung, LG, Hisense, some other local brands all types of ads started to pop out on my Facebook feed. Keep in mind for the whole time I was using Microsoft Edge on the PC and Android with Strict tracking protection, NextDNS as my DNS, and uBlock Origin on PC's Edge browser. I have never seen so many targeted ads before 2021. This is just one latest example for me.
When I used Firefox with first-party isolate/Containers I almost never saw any targeted ads. Containers on Firefox is really a brilliant feature and helps to minimize tracking around the web a lot. No matter what you do on a Chromium browser you simply can't achieve something as good as this.
Chromium browsers are better in terms of security and maybe even in performance by a little margin (Firefox actually feels as fast as Chrome/Edge to me) but for the privacy-minded people, Firefox is still the best choice. It's not by default but can be achieved by minimal tweaking.