User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:49.0) Gecko/20100101 Firefox/49.0 Build ID: 20160802125802 Steps to reproduce: 1. Openend the following PDF: http://de.free.aero/contents/Saison2016-D-300.pdf 2. Clicked some link in the PDF, and rpessed the back-button 3. While PDF.js was loading the pdf again, I tried to switch to other tabs Actual results: The rendering of the other tabs was blocked for several seconds (> 15s), instead only a white page was shown. This behaviour was observerd even with E10S / multi-process enabled. I captured the behaviour in the following screencast: https://youtu.be/KX_FqTK0fhw Expected results: There should be no noticeable delay caused on other, not content loading tabs, especially with e10s enabled.
pdfium conversion should address this.
I upped the "processCount"-pref to 4, yet the issue is still reproduceable. With processCount=4 some tabs stay responsive, while others are still blocked by the busy pdf.js instance. It is almost if the assignment WebWorker-Process <---> Tab is static. So while some Tabs are lucky and get an idle WebWorker, others are statically assigned the WebWorker currently blocked by pdf.js.
Created attachment 8788512 [details] e10s.mp4 Mozilla/5.0 (Windows NT 10.0; WOW64; rv:51.0) Gecko/20100101 Firefox/51.0 I can confirm this issue also. The steps I used are: 1. Launch Firefox 2. In a new tab, navigate to CNN and read several articles 3. In 3 new different tabs - navigate to some websites of your choice (wait for them to completely load) 4. Go back to CNN and click on the Back button 5. Switch to the tabs opened in step 3 Actual results: In step 5 - white content is displayed for a couple of seconds - please see the attached screen cast for more details. Reproduced on Firefox 48 and Nightly 51 with e10s enabled. Not reproducible if e10s is disabled. (In reply to Jim Mathies [:jimm] from comment #1) > pdfium conversion should address this. Also Jim, as you notice in my above steps, I didn't used a PDF, just normal pages. Even if the problem is less visible without using such a big content as a PDF page would contain, the problem is still visible.