>>105587308
You're welcome.
I also made the file menu bar more darker in the css below.
The values can be adjusted, I just made it more darker, picrel is the result, but you can customize the color as you want.
Here's a darker option (as in picrel):

/* Make the background tabs more visible: */
.tabbrowser-tab:not([selected="true"]) .tab-background {
background-color: rgba(160, 160, 160, 0.3);
/* border: solid 1px rgba(207, 207, 216, 0.2); optionally customize the border */
}

/* Make the menu bar more visible */
#main-menubar > menu {
background-color: rgba(192, 192, 192, 0.4);
border-right: solid 1px rgb(160, 160, 160);
border-bottom: solid 1px rgb(160, 160, 160);
}