As part of implementing the private browsing search engine, we should add a UI for setting it.

The UI should be able to be hidden by the pref added in bug 1562922.

Comment on attachment 9094953 [details]
Bug 1563021 - Add preferences UI to allow enabling and selection of a separate default private engine.

Verdi, could you try these builds out please?

https://queue.taskcluster.net/v1/task/SwQeCiXvRvS62NnzSuWIDQ/runs/0/artifacts/public/build/target.dmg
https://queue.taskcluster.net/v1/task/VKJHBDRCTkWLI2vqEZt8vg/runs/0/artifacts/public/build/target.zip

Notes:

• The preference display will just be re-arranged initially, you'll need to set the browser.search.separatePrivateDefault.enabled to true to see the separate search engine.
• The sub-text is currently grey rather than black. That's the default theming for preferences for indented sections. Quite happy to change it if you want, but I left it as it was to being with.
• Only the address bar, search bar and context menu pick up the changed default in private browsing at the moment - the new tab page does not.
• The extra check box for show private search suggestions will be created in bug 1583162.
• I've used the text that is in the design doc, I'm assuming you're signing off on that as well.

Try push: https://treeherder.mozilla.org/#/jobs?repo=try&revision=89ce4f148b8f47ecd46bf525ee1f0a9e5c2b17e5

Comment on attachment 9094953 [details]
Bug 1563021 - Add preferences UI to allow enabling and selection of a separate default private engine.

Hi Mark. Mostly this is looking good. The main thing I see is that when I flip the pref, the "Use this search engine in Private Windows" checkbox is unchecked. It should be checked by default and it's unchecking it that reveals the dropdown to choose a PBM search engine. It seems like it's backward in this build. The other thing I notice that you didn't mention above is that there isn't a link back to the history settings in Privacy & Security. That should be below the search suggestions section.

I also want to note that I can see how you saw that this pref would work differently that what I intended. I think I can fix that with copy. I will bring this up specifically with Betsy.

Comment on attachment 9094953 [details]
Bug 1563021 - Add preferences UI to allow enabling and selection of a separate default private engine.

Updated builds:

Windows: https://queue.taskcluster.net/v1/task/OOUkQQE8RoWs9qcbB1dZ1w/runs/0/artifacts/public/build/target.zip
Mac: https://queue.taskcluster.net/v1/task/GoweYMDORZWEx3zlINGWXA/runs/0/artifacts/public/build/target.dmg

Try push: https://treeherder.mozilla.org/#/jobs?repo=try&revision=2b43135d4a1b4ad23e8e04bac139378e28efec1d

Comment on attachment 9094953 [details]
Bug 1563021 - Add preferences UI to allow enabling and selection of a separate default private engine.

This looks right. Let's go ahead and change that gray sub-text to black though.

https://hg.mozilla.org/mozilla-central/rev/4d973794f0e0

Hi, This issue is verified as fixed in our latest Release version Fx 72.0.2 using this preference browser.search.separatePrivateDefault.ui.enabled set to True in about:config.
This issue was verified on Windows 10, Mac osX 10.14 and Ubuntu 18.04.