I like the new version... although it's interface was stark different from previous versions, and had to get used to it.
It's a bit faster too than the previous versions.
I didn't like the toolbar, had a lot of empty space, and didn't like the placement of buttons too. But, I found that you can remove the empty space, called as flexible space now, by removing it. I also changed placement of icons, like Home, and Back button. I removed the Sidebars icon, and instead put in the Bookmarks there. Now, it's to my liking.
I used very less add-ons... FEBE, Xmarks, Flashgot, ublock origin. Of these, FEBE won't be developed, and I will really miss it.... it was a great add-on, very useful.
They did develop webextension for Xmarks, but it isn't working. It messed up my bookmarks, and of many others too. Also, when I went to the add-on page on Firefox site, it says it isn't compatible with Quantum. I think they are working on fixing it.
There was news that Flashgot would develop webextension, but they haven't updated yet. But, it's not a problem for me, since I used Free Download Manager, and their own extension to catch downloads from Firefox works well.
ublock origin is a webextension now, and is working great.
I am happy with Firefox, and will continue to use it.