modified options_ui for firefox compatibility

[psonghi]

The only change was made to manifest.json.
options_page: is now options_ui:page: to get the options menu to work in firefox.

Tested using chrome version 56.0.2924.87 (64-bit) on ubuntu 16.10
Tested using firefox version 51.0.1 (64-bit) on ubuntu 16.10

[jessicandavis]

Great! How do I install this in FF (pretty noob)? Thank u.

[alexeisolonari]

For anyone who wants Firefox compatibility, check out my fork: https://github.com/lolrepeatlol/BlockClock/ https://addons.mozilla.org/en-US/firefox/addon/blockclock/

My fork uses this patch that psonghi proposed :)