I switched to Firefox ~1.5 years ago and it does everything I need, actually never picked chrome up again. The android version is very good as well, but I just switched to iOS and it's not a very smooth experience there.
Biggest issue for me is not being able to import passwords from Chrome. I have to switch back to Chrome if I need to access some web services quickly, so building up saved passwords in a browser makes it more sticky. There's probably a reason for not being able to do this though.
It also starts to get a bit sluggish when you have a couple (6-7) heavy JS/DOM tabs open.
File download UI could be better. Skip the confirmation dialog, show file and progress at the bottom of the browser window.
JS sluggishness might be because of a recent Firefox Pioneer study. I've experienced it for the past week and in the end I uninstalled Firefox Pioneeer completely because of it.
imho, file downloads are actually great. When you have active or recent downloads - you'll get a nice litle icon on the right from the URL bar. For active downloads it'll show the total progress for all downloads. Once clicked, it will open a small menu with your downloads. When you don't have any recent/active downloads it just gets out of our way. Much better than that ugly bar at the bottom of the window.
I love Firefox but I had no choice and had to ditch it on MacOS. It seems Mozilla does not have the resources to fix these problems.
I use Chrome (logged with GMail) for "work" and Firefox in parallel for all the rest (banking, docs, general browsing).
For a program that has 1 textbox (2 at max if the search box is enabled) I find it difficult to understand what is the thing one has to get comfortable with by taking determined effort.