I was trying to set up a 2nd NB account - logged out and clicked “Sign up or Log in” which brought up the text fields to the right of the button, clicked the username field, but moments later, an image of the app on an ipad and iphone animated up over the form. Clicking the button again just repeats the process.
Firefox ESR 10.0.5 on Win7-64
Gaaah, turns out this is also now preventing me from signing in on my main account. I think I am totally locked out.
Yeah, even if I disable CSS, I can at least scroll way down and find the login box, but as soon as I start typing, some script yanks focus away. Totally unable to log in.
I noticed that too. But I’m lucky because I have my username/password auto-completed by the browser; I just press Enter and I’m logged in. Maybe you can get in by placing your password in the clipboard so you can type your username quickly then imediatly paste the password and press Enter. I think this would work if you’re quick enough.
Hah, oddly enough, that was what I ended up trying, too. It only took me about 3 tries to get my username pasted before focus changed, but it took me almost a dozen tries to click into the password field and paste before it changed. It looks like you have about 750-1000ms to work after clicking to bring up the login panel before it goes away. Had to memorize the location of where to click and practic the timing. 
This can’t be good for new users.
Problem is that I can’t reproduce it. I try in FF on Mac and it works fine. Is it only for users of an old FF?
I experience the bug reliably on the current supported release of Firefox (ESR 10.0.5). It may very well be a non-issue on the cutting-edge Firefox, but I don’t have a copy to play with.
I can confirm it’s not an issue on Chrome, but I don’t use Chrome day-to-day.