UBNT-ouning,: I appologize if my previous post sounded a bit harsh, it was not meant to be. I know you guys do monitor these threads very well, which is actually getting rare for companies these days. Thanks for that.
For me at least, I found a way to prevent it and then to reproduce it.
This ERL is for 1 of my customers, and they wanted me to upgrade it to the latest firmware, and to test what happens when you do a factory reset using the button (and document some things for them). So, I updated it to 1.9.0, and then immediately did a factory reset using the button. After logging back in, I was of course asked if I wanted use the"Basic" wizard. I usually use the CLI, but decided to use it as a starting point (I have no shame in using it...I have to type programming code all day and I'll gladly give my fingers a break).
Later on, I logged back into the GUI, and that's when I noticed the strange problem in Firefox.
Today, I decided to do the factory reset again (still on 1.9.0), and this time when asked to use the wizard, I declined. I closed the browser and re-logged in and it worked perfectly in Firefox. While still logged-in, I went to the wizards page and chose the "Basic" wizard. I took all defaults...the only thing I did is provide a default password, which is required for that wizard. I told it to reboot. After logging back in, Firefox was broken again.
I can repeat this, and when NOT using the Basic wizard, it works for me in Firefox, but when I use the Basic wizard, it becomes broken in Firefox. This problem might be 1 of those where multiple things can trigger it, but for me it happens when using the Basic wizard.