Can't change colourscheme, firefox error returned

[hosalmeer]

Issue type:

• Bug report

Colourscheme can't be changed

Version:

```Version Information
Vimperator: 3.16.0 (created: 2017/02/01 00:55:15)
Firefox:    Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:56.0) Gecko/20100101 Firefox/56.0

##### Description:

Tried to change colorscheme. Same issue with zenburn, ywgx, and molokai. No colour change and the following message in the bar

[Exception... "Component returned failure code: 0x804b0012 (NS_ERROR_UNKNOWN_PROTOCOL)
[nsIStuleSheetService.loadAndRegisterSheet]"

##### Expected behavior:

New coloourscheme, obviously. 

##### Steps to reproduce:

<!-- Include if relevant -->

[SammysHP]

Duplicate of #796.