As we added the new tracking protection icon on the toolbar, we didn't distributed the space accordingly to not affect the visible portion of the url.
Fennec vs Fenix on OnePlus 5T (the red lines represent 25% and 75% of total width)
2. Unused space on the three dotted menu
The three dot menu has a lot of unused space, as you can see in the image below
The issue here is that we are doubling the padding, between the right tab counter and left three dotted menu, creating a huge gap between them.
This is caused because the tab counter adds the same amount of padding to the right as the three dotted menu adds to the left ( tab counter right padding 16dp + three dotted menu left padding 16dp = 32dp padding between them instead of 16dp).
3. Better distribution of the space on custom tabs
As you can seen in the image below we are not doing a smart use for the space in custom tab, there is a lot of space that can be redistributed, to show more url and title.