Ublock: Delete key frequently not working in zapper mode

[tamlin-mike]

uBlock Origin: 1.15.18
Firefox 59.0.1 64-bit, Windows. Multiple tabs open.

There is not solid repro. It happens seemingly stochastically.

Entering zapper mode (clicking UO icon, clicking the zapper icon) works.
Moving mouse around on the page displays the zapper is active and working (it "highlights" elements mouse cursor is over).
Clicking anything selected works as expected (it's removed).
Delete key while hovering over something frequently fails.

I don't know if this is a problem with Firefox, failing to send keyboard events to UO, or UO itself for some reason failing to act, but it's become annoying enough I feel the problem needs to be documented, and the source of it fixed.

Behavior I have observed is that once Delete key works once for a page, it keeps working. This lends credibility to my theory it's a matter of keyboard events. On failure, using mouse to make sure the displayed web-page is active, even selecting some text on it, does not help solve the problem.

[gwarser]

Duplicate of https://github.com/gorhill/uBlock/issues/953
Also https://github.com/gorhill/uBlock/issues/2719

[gorhill]

Beside the focus issue described in these other issues, it could also be another event listener (from the page or another extension) "eating" key down events, and preventing uBO from being notified.

[gwarser]

I googled a bit - Firefox have problems with focusing inside iframe. People suggest to wait for frame to be fully loaded

https://stackoverflow.com/questions/1508348/set-focus-to-iframe-body-content-in-firefox
https://stackoverflow.com/questions/369026/setting-focus-to-iframe-contents
https://stackoverflow.com/questions/14377219/focus-in-an-iframe-in-firefox

[gorhill]

uBO already waits for the load event before forcing a focus on the iframe.

[gwarser]

I cannot reproduce anymore on Nightly 63, beta and stable still affected.

However:

There is not solid repro. It happens seemingly stochastically.

---

OK in Chromium 71, Firefox 64.

[gorhill]

OK in Chromium 71, Firefox 64.

Alright then, closing. A new issue should be opened if ever it's being reproduced again.