Difference between Open and Import
On Pixly, you have two options regarding loading images in. You may Open images or Load them.
When opening an image, all your current artboard will be trashed and everything will be replaced by this new image (or animation) you loaded. If you want to load a previously saved project that has more than one layer and/or more than one frame, start opening the .anim file, otherwise, you'll end up opening just the sprite sheet of it.
When importing an image, all your current artboard will be kept, and this image you loaded will be added alongside as a new frame. As all frames must ALWAYS have the same layer amount, blank layers will be added in case it doesnt match the layer count of your project.
Bonus: Dropbox and Google Drive integration
You can load files form Dropbox and Google Drive on Pixly, everything goes seamlessly. Here is a thing you might want to know:
Google Drive only gives Pixly the permission to view the files you give to it. For this reason, in order to load an .anim file you'll be asked to show pixly where the sprite sheet for that Anim is.