Thanks Dave, it sounds very interesting.
I know that with another grocery app we can add items by sending an email, so this would be great because VC could just send an email for each item. Unfortunately this particular app creates a new shopping list for each email that you send which makes it kind of useless because there is no way to combine all your items into a single list. In this case, you could always let VC keep your complete list, but then you would need to remember to ask VC to send the complete up to date list before you went shopping. Not very practical. I spoke to someone "over there" but I got the usual run-around trying to get them to add a simple feature, even though it would ultimately lead to all my users potentially wanting to use their program. sigh. life.
Anyway, I wonder if the makers of this app would be more responsive to our needs, providing some kind of web or email api. That would be great, especially since this one seems to be cross platform with Android / iPhone etc.
now back to your question. I don't think there is any way for VC to know that Firefox has finished loading a page. VC can load a page itself using scrape and I believe it will wait until the page has finished loading before going to the next action, but that is different. I'm sure a firefox plugin could be written that would broadcast whenever a page was loaded, but I doubt one already exists, and I don't know much about that, having never written any firefox plugins before.
When I have time I'll look into this app though. Maybe there is a way to add items using scrape. Usually this is not so easy though, especially since you need to be signed in and these sites use a lot of fancy css/javascript gui. Finding a way to simply post data can be painful.