I grew up on Ubuntu (8.04, what a great release and gorgeous looking GTK2 theme) and this was the last straw for me. Firefox included as a snap on default just takes too much to open on my beefy new Thinkpad. Off to Fedora for me.
2. Opening them is slow once per boot.
3. It's mystery meat to the highest degree. Might as well use windows.
Real shame because Ubuntu has things going for it that no other distro has. Namely the beautiful font rendering and sane desktop defaults.
I agree with the "mystery meat" criticism though, especially for Firefox they should make the packaging process transparent.
Also, if you want to have a more leisurely pace of browser functionality changes, you can also choose Firefox ESR that still receives timely security fixes.