The behaviour when selecting a URL in the URL bar in iceweasel is inconsisent with the behaviour of Firefox on windows.
As an example, I will use the URL 'http://www.google.com' The behaviour in Firefox on windows is as follows:
Single click in word 'google': caret is placed in word google
Double click in word 'google': word google is selected (this is useful, as it makes it very easy to change a URL to another address) Triple click in word 'google': whole URL is selected.
The behaviour in Iceweasel is as follows:
Single click in word 'google': caret is placed in word google
Double click in word 'google': whole URL is selected (actually, it is split on spaces, but these are rarely present in urls)
Triple click in word 'google': whole URL is selected.
Note: Also seen in earlier versions of Firefox for Linux (from around 1.5).