When I open the style editor, the window is kinda small (likely something I did a long time ago). Is there a way to change it to a larger one (the size of the opened firefox window would be nice)?

Without a doubt, one of the most useful extensions on the web. It's easy to use, robustly functional, and unobtrusive.

Great add-on. userstyles.org website appears to be stable now.

Perfect! I needed something to hide the cookie policy dialog on amazon.it and it took me just one minute to do it using this web-ext.