I don't know if a change was made or whether I needed to clear my cache, but the theme is now working in Firefox on Android for me.
More suggestions:
- I suggest losing the color green for the theme's palette. You already have shades of blue, orange, black, grey (main site colors), and white. If you are going to use green, use it for the "user is online" indicator (does that need to be in two locations, by the way?). Otherwise everything that is green could just as easily be orange... the theme is a little busy or overloaded with colors, otherwise.
- The background gradient is a little annoying the more I look at the theme. It would be cleaner and more consistent to just use a single shade of blue. The logo has a gradient - which is fine - but the forum background doesn't need to. It just gives the page an uneven or assymetric look left to right (almost like one is using a panel with poor viewing angles), and does make it look more dated.
Gradients are fine for UI elements (like buttons), where combined with drop shadows the illusion of solidity or depth helps them stand out and makes the interface slightly easier to use, but in the background it doesn't help anything.