I switched to Firefox again back in 2017, I have 0 issues with it. If anything it's faster and less resources hungry than chrome in my usage. The extension ecosystem is now arguably better with MV3 being rolled out to chrome.
Probably the only annoying thing was learning where the buttons are in the devtools. They're all still there, just laid out differently. It took about a week to get to grips with that.
What exactly makes you say it's an awful browser?
More seriously, I'm a Firefox user since ~2006 but I'm about equally surprised by the statement that Firefox should blow Chrome/ium out of the water as that Firefox supposedly sucks. They're both browsers. I think Chromium is a bit faster in page rendering, whereas Firefox is more open, privacy-friendly, and customizable. Similar to how I wish consumers would not choose an anti-consumer organization (anyone who values a free market and general computation1 should not choose iOS), I think nobody should choose Chrome but, still, I can understand if someone does choose it because they've gotten used to how it works and they're not willing to change. It's about equal in practical functionality that 95% of people use, wouldn't you say? Or in what way is Firefox blowing Chrome out of the water?
¹ https://www.thekurzweillibrary.com/the-coming-war-on-general...
Yet it's still more customizable for users than Chrome/ium is. That there is a particular customization they got rid of is a shame and what you mention in the sibling comment (only works in some contexts) bothers me every day when I try to use mouse gestures on a settings page or mozilla domain and it refuses to work, but those new limitations don't make the statement untrue as a whole
Not really, you've explicitly said this
> Yet it's still more customizable for users than Chrome/ium is
And then rejected the fitting comparison: Firefox (the browser) is not more customizable than Chromium-Vivaldi (the browser)
I also don't see how the engine used for page rendering is relevant when discussing UI