If space is important, have you considered moving Firefox's menus around so it's more compact? The whole point of using Firefox over a less customizable browser is to make it fit your own needs. For example, this is what I use on my laptop:
The most significant improvement I've seen is the ratio of vertical to horizontal pixels introduced by side tabs. I have been using these on my cr-48 for a couple of weeks and I'm completely addicted. My only complaint is that the developer chose a stack metaphor instead of a reading metaphor, so new tabs appear above, instead of below. I and others have complained about it in the bug tracker, so hopefully that gets fixed, but over all, side tabs are a great re-use of all the wasted horizontal pixels on a laptop.