all icons have a consistent style
The icon for the "Give feedback" menu item looks out of place because it has a totally different stroke width than the other icons.
There are also other inconsistencies. For example the "Help" and the "About Fenix" icon - both have the circle around them and both looks different.
But the icon of the "Give feedback" menu item is the most striking example because it doesn't fit at all.
UNITO-UNDERSCORE!20190406-151443!
No, it's not a bug. Fenix is a mozzila project and uses mozzila's icon style. The icons are separated into two parts (mobile and desktop). Desktop has wider icons while mobile icons are slimmer but there is less of them. The icons you are talking about haven't been designed yet. They will probably update it in the future. They are awere of this and I hope it is enaugh to close this issue.
No, it's not a bug.
It doesn't matter if we call it bug or not. It's only labeled as bug because I used the GitHub template "Bug" to report this issue and I used this template because the sections make sense for reporting such an issue.
and I hope it is enaugh to close this issue.
Why do you hope that an issue get closed if it's not solved? 😳 This is an issues tracker. In issues trackers issues will be closed if they are resolved / tracked in another way / won't be fixed / another good reason. Maybe these are not the final icons and maybe it's already known to someone but I can't find any other ticket about this. If that's the case then someone from Mozilla will tell this. But your comment is not very constructive.
K. But make sure this isn't a dublicate
The cause is that Fenix is using a mixture of Desktop and Android style icons.
See: https://design.firefox.com/icons/viewer/#
The platform toggle is on the top-right.
FWIW, the mockups use different icons: https://mozilla.invisionapp.com/share/8ZQVRNUJW3H#/screens/350752852 that are more consistent
The invision link is password protected.
But good to know that there are already mockups with more consistent icons. :)

I pulled some newer vector icons in from the design docs. Closing but let us know if you see any other icons out of place! Thanks!
It's much better now, thanks!