QA steps
To reproduce:
- Make sure you have an iOS device. iPhone XS Safari. (browserstack will do!)
- Visit http://reading-web-staging.wmflabs.org/wiki/Prime_Minister_of_Australia
- Make sure you are logged in
- scroll to bottom of page, click talk button to open the Talk overlay
- open a discussion
- scroll to the bottom of the page
- try to continue scrolling further down — at this point one of several things seems to happen:
- the page freezes and I can't scroll back up
- the page header disappears
- a gray border/line appears, and is fixed towards the bottom of the screen
Developer notes
Bartosz has a fix here: https://gerrit.wikimedia.org/r/#/c/mediawiki/extensions/MobileFrontend/+/489222/ which fixes out handlers for 'touchstart' and 'touchmove' events to not be passive (they are passive by default in recent browsers, which means preventDefault() doesn't work).