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.
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.
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 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.