All I want is a bare metal browser. I don't want an operating system and I don't want to run chromium OS. It would be great to see a bare metal browser that implements something like Gecko.
Without writing the entire browser from scratch, I don't personally think there's much point to this. I suspect if you traced down the library/runtime requirements for Firefox and reimplemented them in a bare metal runtime, you'd end up with something remarkably complex and not much simpler than Linux + runtime in the end.
This is assuming you want a full browser capable of everything Firefox and Chromium are, which includes things like WebGL. If you cut out components, you can definitely reach a point where a bare metal browser is sensible, the question is how much are you willing to sacrifice from "web standards" and how much work are you willing to do reimplementing a kernel, TCP/IP stack, device drivers, etc...
I cannot imagine a unikernel with all the drivers ready for a reasonable variety of PC hardware, unless it's able to reuse Linux or at least FreeBSD as a source of drivers.
Linux also uses grub as a bootloader, and has never been called slow.
> The resulting GRUB module, mezzano.mod, is largely the KBoot Mezzano loader code, ported to use GRUB facilities for memory allocation, disk access, etc. It’s feature-complete, so I released it to Sourcehut. (I’ve only tested it on Libreboot GRUB, not GRUB loaded by other firmware implementations.)