ColorizedButton is a Firefox addon, can change the orange main menu button into any color you want.
You can change the private browsing and the "normal" browsing color separately, both in ColorizedButtons Preference menu.
Hint: This AddOn doesnt need a Firefox restart, but while testing I saw that the preference button in AddOn list is missing sometimes due to the restart thing. Dis- and Reenabeling caused it to appear again.

Requirements:
* Firefox

The license of this software is Free, you can free download and free use this browser plug-ins software.