If I start to edit a string value and want to cancel I press escape. Nothing happens. It would be nice if this undid my edits.

Also, or alternatively, a "Cancel" button could appear next to the "Save" button, to allow me to dismiss the edit box without saving my changes.

It turns out that clicking "Edit" on a different preference will have this effect: it dismisses the current edit box without saving changes. But this is non-obvious: I wasn't at all sure it would be possible to start editing a new preference without first saving the current one, and I certainly couldn't tell in advance whether doing so would or would not save the edited value of the current one.

To put things in perspective, most edits of text fields would be from "0" to "1" or similar.

We're not really concerned about making this the best user interface possible, it just has to be good enough to allow people to perform the task.

That said, canceling the edit when pressing ESC would be a nice to have, I think we could accept a patch to do that with a specific regression test. This isn't high priority because a workaround to get rid of a stray click on an edit button would be to just search again or reload the page, clicking Save without modifying the value, or use the Undo command in the textbox.

Hi, I am willing to work on this, please assign it to me.

Thanks for working on this! As noted in the review, this requires a test case to be written. If you have a mentor, they can help you with it.

New about:config is not by default in 67 -> disabled.

Push with failures: https://treeherder.mozilla.org/#/jobs?repo=autoland&group_state=expanded&resultStatus=pending%2Crunning%2Csuccess%2Ctestfailed%2Cbusted%2Cexception&searchStr=os%2Cx%2C10.14%2Cshippable%2Copt%2Cmochitests%2Ctest-macosx1014-64-shippable%2Fopt-mochitest-browser-chrome-e10s-7%2Cm%28bc7%29&revision=65435277ebd7ce29eebb9c2dadb22828d35eaa57&selectedJob=266581594

Failure log: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=266581594&repo=autoland&lineNumber=2167

Backout link: https://hg.mozilla.org/integration/autoland/rev/f5dd266a1d0460abf9d2df433ad08e590edbd941

https://hg.mozilla.org/mozilla-central/rev/90984e8cdaec