There's plenty to like about Firefox, like the Awesome Bar, has better bookmarking, is able to handle a huge number of tabs, has the "Multi-Account Containers" extension (with its offspring, e.g. "Facebook Container"), or the "Tree Style Tab" extension, just to name a few.

Also that it's not Chrome or based on Chromium is reason alone to like Firefox, because we need diversity for healthy web standards. That Chromium is open source is a red herring and open standards are more important.

I know developers have been preferring Chrome and for good reasons, but I've switched back to Firefox for the last 3 years and personally I find it hard to use Chrome these days, because Firefox has a better UI.

The only downside is that Chrome's dev tools still has some capabilities that Firefox lacks, but Firefox has been improving a lot, as you have seen.