User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:51.0) Gecko/20100101 Firefox/51.0 Build ID: 20170201180315 Steps to reproduce: Navigate to http://ftp.acc.umu.se/mirror/opensuse.org/tumbleweed/repo/oss/ChangeLog . This file is a 63.1 megabyte text file without any mime type. Content-Length is present. Reproduced on both Linux, Win64 and macOS. Win64 instance has Electrolysis disabled due to plugins, no idea about the other two victims. Actual results: At first, the browser responds slowly to scrolling and eventually just decides to make the whole window not respond. After a good minute or two whatever it does completes and the file is viewable in a reasonably normal fashion. Expected results: In a perfect world, the view of the immediately viewable content should respond smoothly and jumping around might cost a bit. It'd be swell if the browser didn't completely wedge.

With a fresh profile that has multiprocess enabled (according to about:support) the page renders a bit more than a windowful of the content, any scrolling shows white background. Jumping around the file results in white content until a windowful is rendered. This continues until the browser is "done" with whatever it was busy with, and the file responds properly afterwards. Human-wise, the experience in multiprocess is "better" as the rest of the browser tabs/windows keep responding at least, but sadly Electrolysis isn't everywhere thanks to addons.

Moving from Core::Untriaged to Core::General https://bugzilla.mozilla.org/show_bug.cgi?id=1407598