Epiphany is my current browser of choice but there have been a couple of odd (and recent) behaviors that I'm struggling to correct.

1. When attempting to launch the browser from an email hyperlink, and if Epiphany has already been launched for another reason and is currently running, the linked page loads normally in a new Epiphany browser window. If, however, the browser is not running I get a message that states something like "...mozilla initialization failed. Check your MOZILLA_FIVE_HOME environment variable" and the browser will not launch. It's an annoying behavior that I would like to understand and correct.

2. In Epiphany, when I add a new bookmark, the site name is saved but not the web address. Of course, I can add the address manually through the properties dialog but I shouldn't have to do this either.

A remove/reinstall is an option, but why have these behaviors popped up in the first place? I have installed several applications over time, the only problematic one being OpenOffice 1.1.2.

I am not sure but I would guess that your browser is normally launched by a script that sets the relevant environment variable. It seems as if implicitly launching the browser is running the executable. When it is already running then you get another window of the running instance. When it is not yet running, the initialisation code does not find the required environment variable.
Try looking at what actually is run when you launch the browser explicitly, and simliarly what the association is for a browser.

Thanks for the resolution. I was explicitly running the epiphany script while I should have been running 'epiphany %U'. Problem solved.