If GP is talking about the same issues that I frequently run into, then I'd say that's almost definitely not the case. I continue to use Firefox iOS despite these issues because I like the shared history and bookmarks with my desktop, but they do annoy me on the daily.
A couple off the top of my head...
If you do something to trigger a page load, like open the app after it has been suspended, and while the page is still loading you touch the address bar to enter an address or pick one of your "recently visited" or whatever, you will be surprised when the page finishes loading and replaces the view. It replaces the view, but you're still in the "navigation bar selected" state, so you can get them back without hitting the tiny back chevron and tapping the address bar again. I doubt this has anything to do with how they are forced to hook into WebView. It's just sloppy handling of async code.
Speaking of that same view, the top four links shown there as favicons are in a constant state of flux. Generally, it's HN, Reddit, Google News and whatever else I frequently visit, but sometimes for reasons I don't understand they get completely jumbled into something else. The icons are constantly disappearing and reappearing. It's not a big deal, but it feels unstable. I'm not sure why they don't just let me pick bookmarks to save on this view instead of automatically picking them for me. There are many things I would like to have available at a single tap, but I don't visit frequently enough to make it into my top four. Like trash pickup schedule. I don't read that several times a day, but when it's time for the trash truck to come and I forgot if today is plastic or paper recyclables, I'd like to have that link bookmarked for quick access.