[ubuntu-uk] Firefox not getting focus

[mac]

I notice that recently that when I click a URL in an e-mail, or select 
an item in Liferea (ver 1.6.0 in Karmic; 1.6.2 in Hardy), a new tab 
opens in Firefox (with Firefox already running), but Firefox does not 
get focus as it once did.  Instead, I have to bring Firefox to the front 
manually to read the item.

This behaviour is new (after the recent update to FF 3.6.7?).  In 
about:config I have

browser.tabs.loadInBackground = false

Searches suggest that the default behaviour I used to find useful - 
switch immediately to FF when I click a URL or Liferea item - has been 
viewed by some as a bug.

Can anyone suggest how I might restore the former behaviour?

mac