Rated 5 out of 5 stars
Essential addon when having more than one monitor. In the last version the WM blue icon vanished (the button is blank) but it still works.
Edited: Thanks for the reply! After some tests I've found out that it only happens when I have the "Classic Toolbar Buttons" addon enabled, so I think that's the cause.
Thank you for the positive review.
Perhaps you could let me know whether the icon is invisible no matter where the button is placed (tab bar, navigator bar, panel), what your OS and Firefox version are and whether you have any (complete) themes installed. This information may help me to find the cause. I may need to add some CSS rules for certain themes, given that the icon is pure CSS.
Edit: Classic Toolbar Buttons did not seem to have any negative effect on my system (Firefox 38 on Windows 7). Are you able to identify precisely what option causes this?