When moving around the config pages of my Billion 7800N I have been getting salmon pink error pages with a 400 Bad Request error message. A quick browse on the Billion forums revealed this to be a problem others are having when browsing the router with FireFox v15.0. I am using Waterfox v15.0, the dedicated 64 bit version of FireFox. I fired up Internet Explorer and browsed the router with no errors at all. So if anyone has this problem the solution sadly is IE until FireFox is fixed.
Customer and Forum Moderator. Windows 10 Firefox 64.0 (64-bit)