I didn't find the performance gap really high when I switched from Chromium to Firefox. Even on my shitty old laptop, Firefox works fine. I have to admit though that it uses way too much memory.
I do agree with your 3rd point though. History has taught us that defaults matter a lot. Firefox isn't a default anywhere apart from linux distros and FirefoxOS was a failure.
It's hypocritical to call your service "privacy friendly" and then require the use of a Google/Facebook/GitHub account to log in. I kinda understand the reason why they do this, but they could have at least allowed you to use a more private email provider.
FIRE IN THE HOLE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!