Confirmed it is not Classic Theme Restorer (disabled and restarted) nor theme (tried a few all the same) and cannot find anything in about:config. It is NOT highlighted text color setting.

Any help please?

Thanks. ~Bob

Does this only happen in the Session Manager extension or also elsewhere when you hover buttons?

Not only hover, cor-el, but default focused buttons as well. And not everywhere, but most windows style dialog boxes.

Let's see:

Tab Mix Plus options buttons Page Info NOT FIle - Open File BUT Page Setup

Many more I am syure, but perhaps this is enough?

I searched about:config for #ffffff but nothing showed as the culprit/

Thanks for the help.

~Bob

Pointed out to me by another user, the icons on the hamburger menu are now black, as well. Not attractive.

A plugin developer provided a Stylish code to get my b;lack text back, but I should not have had to do that. Surprised your Beta testers don't see these things. Or maybe they are by choice. Don't know.

~Bob

I don't see either of those issues in Firefox 51.0 -32-bit on Windows 7 -32-bit, I wonder if it might be a "64-bit thing" only?

You can try a different Windows theme and Windows background image (wallpaper) to see if that helps.

Not all Windows themes might be compatible with current Firefox releases, so you may have to try out other themes if the one you currently use doesn't work as expected.

A browser should not be dependent on a windows theme, don't you think? Nor was this an issue before 51 with the same windows theme I have been using since day 1.

~Bob

I came here to ask about the same thing. Every button that is the default option or that is hovered with the mouse cursor has white text instead of what it should be (and always has been until this FF release), which is black in this case. It even does it on the FF profile manager if the --profilemanager switch is set.

I've done some experimenting to determine the scope of the problem. I created a blank (new) profile in FF and loaded that-- it still happened. It's not an addon, pref, or FF theme.

I am using Windows 7 x64, FF 51.0.1 x64, with a custom Windows theme (using the Windows theme engine, not Windowblinds or any other third-party theming program). That custom theme seems to be key.

I tried it on another PC (also running 7 x64 and 64-bit FF, as well as the same custom theme). The same incorrect colors were present on default and mouseover.

I tried switching to the default Microsoft "Windows 7" theme (aero.theme), and the button text was colored properly.

I then tried all of my custom themes, one by one, and every one of them had incorrect text color rendering on some of the buttons in FF. Most had the same as what is described here; button text that should always be black was white for default or hover, but one darker theme that was supposed to have white button text for all buttons instead had black button text on the NON-hovered or default buttons.

I then copied the "Windows 7" aero .theme and directory to form a new theme called 'aerotest', renaming and editing filename references as needed, and selected the new theme in the Windows Personalize dialog. Again, the buttons in FF showed up incorrectly, even though the theme is functionally identical to the default "Windows 7" aero theme that works fine.

For whatever reason, Firefox is pulling the hover/default button text color from the Windows theme's text highlight color instead of the button text color. (For the sake of clarity, the highlight text color is the color of the text itself, not the background, if you click-drag the text-select mouse cursor over text, as if you were going to copy and paste that text somewhere.)

Thanks SO much for posting. I think the Mozilla engineers usually figure it is only me when I post issues. Especially when they do not reproduce it.

I hope this one gets fixed.

And also notice the icons on the hamburger menu are now a very unattractive black.

~Bob