Firefox

Because of that, while you may be choosing a "privacy-focused" browser like Firefox, you're also getting substantially less third-party app support, and a higher chance of websites not performing as intended (like legacy banks or modern sites using newer technology). It simply comes down to there not being enough marketshare for web developers to focus on making everything work properly in Firefox as it only accounts for less than 3% of global marketshare.

Given this foundational difference, it means that the millions of Chrome extensions that are accessible to people, are not in Firefox, unless they rebuild it for Firefox, giving people less options if they choose Firefox as their primary browser.

For that reason, most people who use Firefox also use a second browser as well (typically based on Chromium), like Arc Browser, Chrome, or Brave for when they need full features and functionality like full Chrome Extension support.

That said, while they are a non-profit and privacy focused, they still make the far majority of their money from Google ($500M/yr) by having Google as the default search engine. So if you want to be a sustainable browser, you really need to just make a deal with Google in some way.

Some argue that Google is in some way strategically paying Firefox at this point just to make it seem like Chrome is not a monopoly.