Aside from the slow startup, which doesn't bother me, it's good.

The tabbed browsing is an often welcome alternative to Microb's opening in foreground windows which keeps you from continujng to read the page you're on, adds more fingerstrokes to get to other windows instead of tabs, increases risk of accidentally closing a window in Microb, etc. I do use Microb for quick checks of single page sites like local weather, etc.

Where are bugs reported?
This Fennec beta I downloaded:
1. Lacks zoom via volume rocker
2. Shift and blue arrow keys on hardware keyboard are not sticky

The fact that installation of the beta via the official Fennec webpage is "broken" makes you wonder if Mozilla really cares about the product.