The firefox that was built as part of the recent rawhide mass rebuild doesn't work right for me here. There's a bunch of visual artifacts, tabs don't update the content area when you click on them, fonts are strange and ugly. Downgrading to 51.0.1-2.fc26 and everything is back to normal. I can take a video or the like if you aren't able to replicate.
*** This bug has been marked as a duplicate of bug 1422532 ***