I don't know why people take my comment so badly. I dislike Australis, not Firefox.
I have been using nightly builds of Firefox for years, with some short breaks when an unwanted change was being introduced. Sometimes the change was discarded, other times I decided to embrace it. I got used to the new downloads panel, for example.
Up until now, I have been able to revert all the changes they made, where I didn't want them. A big example of this is they keyhole back/forward button. I keep the Home button in between back/forward and the addressbar, so that they don't merge. In contrast, I did like the stop/refresh being combined, and I was ok with them being put into the addressbar. I use F5 to refresh anyhow.
But above all, I value customization. That's why I use Firefox, and why I choose to use it instead of Chrome or IE11. I like to see things the way I want them, and they don't usually match the designer's choice. As I said, up until now, the changes were either positive, or they did not affect me enough to reject them. Australis is something else.
With Australis, they are removing customization, in favor of a more unified UI across all devices. This has two issues, in my eyes, which are both based on one simple fact: I have a very large monitor, at 2560x1440px. And it could still be bigger. I have enough space in my screen to hold a webpage, multiple addressbars, and in those, keep all the buttons I would ever use.
I don't want an UI optimized to reduce space. I don't want an UI that looks the same in my desktop and my tablet -- they are very different devices with very different purposes. I want to put things where I like them. And they are taking that away from me.
By my principle, I want to use the closest thing I can get to the Firefox I Used To Love. So yes, PaleMoon is my top alternative so far. And don't you dare talk about chickening while posting as AC.