This is pretty much an internal browser issue that'd be literally impossible to work around. I've been seeing some blurred text on various sites since one of the third-point releases of Firefox 36 was released, though it goes away within a second or two after you start moving your cursor around the site and scrolling.
I've just seen this happen on FF 37.0.1 on windows. Also after clicking the 'save changes' button, the text turned white
Definitely appears to be a browser issue, as lowering the font size to the point where the width of the text on the broken buttons matches the cancel button makes them appear correctly. Additionally raising the font size of the cancel button to 15px or more breaks it as well.