Maybe I'm not as critical about the UI, but I have both browsers open at the same time so I took a second to compare them.
Both browsers have a row of tabs. Below that is a second row. The left most set of buttons is navigation (back, forward, refresh, etc), then the address bar, then on the very right of the row is a set of buttons for extensions, settings, etc. The remaining portion of the window is the webpage. I'm just not seeing many differences. The view of recently downloads is different, but nothing that bothers me from either one.
I also just compared how both browsers displayed HN main page. Slight differences in color of orange and font weight, but only noticeable if comparing both directly (and besides devs, who does that?).
So I guess I'm asking what about the UI/UX is bothering you. I'm almost hesitant to ask because I'm sure if you point something out that bugs me, I'll never un-see it.
The lack of smooth zoom support has been a known deficiency in FF for the last seven years (https://bugzilla.mozilla.org/show_bug.cgi?id=789906) and has yet to be addressed.
Otherwise I completely avoid chrome because of the privacy issues, and because firefox has 'containers' and is a little snappier.
I dislike Firefox's zooming behavior. I have to zoom into websites because I have poor vision. Chrome's zoom behavior has been extremely natural for me, and easy to adjust to. When I used Firefox I attempted to use 'vanilla' as well as an extension that aimed to improve the zooming behavior by separating scale of text from scale of other elements, etc.
I was unable to find a solution that worked for me. I hated using the extension, which itself had a pretty bad UX, and I couldn't get preferences to save properly for individual webpages.
I can't use a browser with poor zooming behavior, I rely on it too much. As I write this I am zoomed in 250% in Chrome, for example.
Those pet-bugs or pet-nits are, in my opinion, the huge thing that keeps people from moving (alongside the perceived friction of moving data over). I wouldn't read too much into mine.
I don't know how Chrome does it, but needing an extension sounds like you didn't try the built-in text zoom: https://support.mozilla.org/en-US/kb/font-size-and-zoom-incr...
I think it's the 'second level' of UI stuff - menu's behind buttons, settings pages, things like that. I think Chrome does a good job balancing 'advanced user' and 'basic user' stuff. Firefox feels a little too 'dumbed down' for me.
I'm honestly trying hard to put a fine point on it, but it a lot of it just feels 'off'. I'd love a very minimal-design, maximum function look into it.
As far as dev stuff, I'm really only familiar with Firefox after Firebug was rolled into the browser so that it is similar to Chrome with a Cmd-Option-i key press. I hear people stating that the dev tools are still very different. All I really ever use it for is seeing how the DOM is changing in the inspector, looking for output in the console, and see what files are doing (404,200,500, params/response, and CSS values type of stuff. Both browsers do what I need in a way that I can't tell the difference.
On top of that, various parts of Firebug's console UI was better than either one's current console, mainly in how it displayed data.
So on the color thing, one of our designers noticed and I looked into it. Turned out to be an open bug report for Chrome(ium? I forget) where it's using the wrong color profile for css, and resulted in images not matching borders and backgrounds.
I found that I actually like the UI in firefox after customizing it. For me it may have been easy because I use sway (i3 clone on wayland -- clone is the best, it is actually more / better than i3). But it really ended up looking nice[0]. I found I could customize more things that I could on chrome, including the start page.
In any case, if you don't switch, I urge you to give it 15 mins and tinker with the ui config and a home page config. You can rid your self of alot of weird chrome bits that I think most find ugly and make it look smooth.
Further more, you can set up your own sync server and sync all your stuff to a safe spot.
I don't have a screenshot right now, but it's just as you might expect, the whole tab line is removed (the nav bar line with menus comes to the top instead). [This post](https://www.reddit.com/r/firefox/comments/736cji/how_to_hide...) talks about doing the same thing in the context of tree-style tabs. Good luck!
One annoying thing is that current versions of Firefox seem to rely on disk I/O too much, so if it's busy, you can't really do anything (switching or creating new tabs is greeted by spinning loading circle that takes a long time to happen).
I'm not saying anything in favour of or against these decisions, they're just what I remember reading people complain about over the last year.
edit: typo and clarification
It's built on top of Chromium so has the same UI/UX as Chrome, including dev tools. And it does ad blocking out of the box, no need for an extension even.
Switching is a pain, and I don't like Firefox's UI/UX. I'd switch if they did this because I value the extension very highly, but I wouldn't be happy about it.