Like many of you, I had an issue with Firefox and WindowBlinds not skinning it correctly where the min/max/close buttons became transparent and thus couldn't be seen. Today I installed a new skin on 4 of my PC's. I decided to try to set all 4 PC's to be the same, where FF would not use the OS title bar nor the FF button, and instead display just the menu across the top. 3 of those PC's where fine, but on the 4th the buttons were not visible (I know this issue has been around for years, I just dealt with it differently until today). Since I run the same version of FF (56.0.2 64 bit), the same FF theme (Dark Bliss) and the same version of Windows (8.1 MCE 64 bit) on all my PC's, I figured it had to be either a hardware issue or something software related on the one PC that was interfering with the skinning. Since I have 2 of my PC's running side by side via a KVM, I can easily compare screens whenever I need to. While in Customize mode on both, I noticed the one PC that wasn't skinned correctly had some extra space between the tab section and the address bar. Turns out that was just from a bookmark menu being in the wrong spot and had nothing to do with the skinning issue. But in the meantime, while still in Customize mode, I decided to grab the window and move it around. For some reason WB really didn't like that and made the tabs and borders almost completely transparent.

I dragged the FF window again and made sure it was at the top of the monitor screen, then restarted FF. I was expecting the worst, but was very happy to see that everything was skinned properly and I could now see the min/max/close buttons. I haven't restarted the PC yet, but I did close and launch FF again, and even went back into Customize mode and things are still good.

For anyone having the same skinning issue, give this a try. Obviously I can't say for sure it will fix the issue for you, but it's worth a try.