I never left! I've been using Firefox nonstop since 2002. For the most part, I was a Netscape Navigator user prior though had nothing against IE and sometimes used it. Since Firefox was 'Phoenix', I've stuck with it and only randomly (once every few years) checked in on Chrome. I never really did care for it, and can't say I've ever had any issues with Firefox, even in the supposed dark ages. It has been impacted with Google's use of the Shadow DOM v0 API, and probably Mozilla's own mistakes, but I never felt it was "slow".
To roll out the welcome mat for any new or returning users, I have some general suggestions.
Consider the following extensions: Containerise; Decentraleyes; HTTPS Everywhere; Livemarks; Privacy Badger; Redirect AMP to HTML; uBlock Origin.
For privacy settings: set custom privacy settings to block trackers 'in all windows', block cookies from all unvisited websites, block cryptominers and fingerprinters. Of course enable 'Do Not Track'. Then block all new permission requests for location, web cam etc.
Lean towards whitelisting sites that you do want these settings, as stringent privacy settings like this can in rare instances, break sites. The only example I've ran into is during NCAA March Madness and the site used to watch the games, but you may find others.
Random bits: I'd also suggest enabling the dedicated search bar for quick DDG bang updates. I also give Mozilla some information so my preferences can be added to the collective as to not be removed at some point down the road. Yes to 'Allow Firefox to send technical and interaction data to Mozilla', 'Allow Firefox to make personalized extension recommendations' and 'Allow Firefox to send backlogged crash reports on your behalf'. Can't say I suggest Firefox Studies though, that's one thing Mozilla rubbed me the wrong way with.
With all of that and your own further customization to make it yours, you should be a happy Firefox user. :)