I was testing macOS High Sierra Beta, and I used Firefox Nightley 58 until yesterday. The close/minimize/maximize buttons dissapeared on the light and dark theme, while default showed an imperfect black round corner and green decoloration.
Today I upgrade to High Sierra final release, and change browser to Firefox Quantum, 57.b03. The problem persists. I didn’t have the same issue in Firefox Nightley 58 in Windows 10.
Yes, there seem to be a number of issues with Firefox and High sierra. Here’s a bug that tracks all of the issues, it might be interesting for you to peruse, maybe you can help by testing the fixes when they are in Nightly and letting Firefox developers know if the issue has effectively been resolved: https://bugzilla.mozilla.org/showdependencytree.cgi?id=1379811&hide_resolved=1
For the record, this is not directly related to Developer Tools 