I don't think that the timing is all that relevant, though. This has been a gradual process over several years now.
The main point is that it wasn't so much what the other browsers and their vendors did that reduced Mozilla's influence, but rather that it was what Mozilla did (or didn't) do that has resulted in Firefox's decline.
Mozilla stopped leading, and instead decided to follow Chrome. While doing this, they've bungled major Firefox features, ranging from automatic upgrades to the UI design, time and time again. They've neglected to sufficiently resolve long-standing resource usage problems. They've ignored feedback from disappointed Firefox users for years now. They've ignored that this direction obviously isn't helping to prevent users from leaving Firefox, while at the same time it's driving a lot of users away, and furthermore it isn't really bringing in any new users.
In my opinion, Mozilla has been its own worst enemy these past several years. They've inflicted more harm on their own cause than any external opponent or competitor could have ever hoped to do.
Whether their choices to 'be more like Chrome' were appropriate responses or not you can debate, but dating their loss of influence or market share to after they decided to 'imitate Chrome' is a mistaken timeline.
Personally, I'd say their loss of market to share from Chrome came from a few things:
* Google's ability to promote Chrome was huge, since so many people look at google every day. This is huge, and perhaps we could just stop there, but...
* Firefox had become bloated and slow and a bit crashy. It's just true. Google had the resources to write a high-quality new browser (which is pretty huge), and their browser was really really fast and really really stable compared to FF. (It is no longer so stark a difference, cause FF has much improved on speed and stability, and Chrome, as it continued to be developed got the inevitable bloat and bugs that software does. Although Google writes pretty good software, and Chrome is no exception).
* FF just wasn't innovating much anymore in features, for users or developers. There wasn't a lot of (non-ideological) reason to use it, if something else came along. Developers matter because they influence other users (in part by designing their sites with certain browsers as their main testing environment), and developers aren't influenced as much by the fact that google.com tells them to download Chrome. But I think FF lost significant dev market/mindshare to Chrome too, in part because Chrome's dev tools were way better than FF's at that time.
Now, if Mozilla made the right or wrong choices to try and recover, we can argue (I think overall they've made a lot of the right choices for the hand they were dealt), but at the point they changed to be 'more like Chrome', it was a reaction to already having lost a huge amount of market share. If they had kept on the course they were on, I think they'd have lost even more by now.