Have a look at the screenshot.
I think this is happening because the history buttons are of type type="menu-button". This causes us to pick up some style rules from toolkit which aren't working well with the new theme I think. This same bug is present with the print and mark toolbar buttons as well which are also menu-buttons.
(In reply to comment #2) > I think this is happening because the history buttons are of type > type="menu-button". Changing all buttons from type "menu-button" to "menu" solves the problem. But this behaviour will break all Add-ons using buttons from type "menu-button".
Wahhhh, be carefull. Buttons from type "menu" (see the tags button) don't have the optical separator between the buttons icon and the small down triangel. Some menu-buttons (see tags button) open the menu by clicking the button (it's not necessary to click explicit the triangel). But other buttons (see my extensions "MagicSLR" or "Allow HTML temporary" distinguish between clicking the icon OR the triangel. Clicking the icon has an own function, clicking the triangel opens the menu. We should save the separator line between the buttons icon and the triangel. Or we need a new different button type in CSS, which has the separator line. This would give us the option to distinguish between different menu button types.
And one more thing. Button type="menu" _breaks_ the classic menu buttons. For example the button "Mark" had an own function in the past, when I was clicking the button itself (mark read or unread). Only clicking the triangel opened the menu in the past (the same as in my Add-ons). Now using button type "menu", the button "Mark" is no more functional - only the menu opens. In my previous comments, I wasn't aware of this fact. So we _must_ save the button type "menu-button" and correct the CSS.
the latest patch in Bug 349565 fixes this problem.