User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:47.0) Gecko/20100101 Firefox/47.0 Build ID: 20160623154057 Steps to reproduce: Press any key (other than Esc) while autoscrolling. Actual results: Autoscroll doesn't respond, continues scrolling. Expected results: Should be able to escape an autoscroll using whichever key is most convenient/ergonomic (i.e. any key on the keyboard, not just Esc). Particularly handy when jumping between autoscrolling and arrow key/spacebar navigation. This is the behavior of Chrome's autoscrolling, and is sorely missed when in Firefox.
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:51.0) Gecko/20100101 Firefox/51.0 I have tested this issue on Windows 10 x64 with the latest Firefox release (48.0.2) and the latest Nightly (51.0a1-20160831030224) and managed to reproduce it. When autoscrolling on a page, using the keyboard, you can only escape autoscrolling by pressing the "Esc" key, pressing any other key won't respond.
Autoscrolling is implemented in toolkit code, toolkit/content/browser-content.js