I updated Pale Moon to version 27 the other day, and now the title bar is not painted except when using default WB windows10 theme. Already posted at their bug section.
Three options right now :
1) Switch over to Firefox which does skin properly
or
2) Rename Palemoon.exe to firefox.exe which will make WB think it is Firefox and enable compatibility for how it handles its titlebar.
or
3) Add an exclusion to make WindowBlinds not skin palemoon.exe
Please note that option 2 will result in some poorly painted titlebar text which is due to a Firefox bug fix which PaleMoon does not need.
I will make sure the next WB update considers PaleMoon to be Firefox complete with all Firefox's quirks other than the one causing bad titlebar text.