Firefox also gave "something went wrong" errors on some pages (e.g. https://old.reddit.com but not https://www.reddit.com) which corresponds to the Web Content segfault in my log. Same pages loaded without any problem on Chromium. Yes, I had added every update and was also using ffmpeg from packman. Unfortunately I wiped the machine and packed it away, so I'm not sure I will be able to give more information. The gdb backtrace didn't say much (from memory 0000000000000000 at ??? if I'm not mistaken).