Addon install flow can be improved.

In current:

- button modifies existing tab
- button installs addon directly.  Maybe it should take you to the AMO page instead?  Neither option feels awesome, because the AMO page is terrible.
- copy is 'obvious' and colloquial (re #114)

Why these are problems:
- they only way to 'succeed' on this is to directly install the addon.  It feels like 'succeeding' should be equally low risk on all the variations.  Right now, it seems like going right to install is a VERY HIGH BAR.  

Proposal:

- title:  "Improve your Firefox", maybe?  
- message:  "The 'Quick Mark' addon makes bookmarking faster".  
- button text:  -> "learn more" -> amo page in new page.  In an ideal world, maybe doing the addon would be better (UI), but I want the 'success rate' to be higher here.