The pref to enable is browser.urlbar.update2.tabToComplete. We also need to have the feature approved by Product first.

There might be a fair number of tests to update. Any test that installs a test engine then autofills example.com will probably have to be updated. Most test engines have the template http(s)://example.com/?q={searchTerms} and so a tab-to-search result will be served.

Product says this is good to go in Nightly.

Initial try run of the urlbar tests with tab-to-search enabled: https://treeherder.mozilla.org/#/jobs?repo=try&revision=11aba1fd9802ecbc5938723cb6e284a9acbc3dbe https://treeherder.mozilla.org/#/jobs?repo=try&revision=4653871a07cc99253f69c48347245b72b3275b2e

New round: https://treeherder.mozilla.org/#/jobs?repo=try&revision=2de70d799eb0d0f4a5ae3d2c0b76c96bc7a34bbd

Tests are passing: https://treeherder.mozilla.org/#/jobs?repo=try&revision=2de70d799eb0d0f4a5ae3d2c0b76c96bc7a34bbd

https://hg.mozilla.org/mozilla-central/rev/c25899d7b631

We can confirm the feature is enabled on Nightly. We verified using Fx 83.0a1 (2020-10-13), on Windows 10 x64 and macOS 10.13.

I love this feature, thank you for adding it. This will be a big productivity booster for me.

However there is a somewhat annoying new change which seems to be related to this one.

Consider the following workflow:

1. Type a search query in the address bar.
2. Hit [down arrow] repeatedly until one of the search engine icons at the bottom is highlighted (next to "This time, search with:")
3. Hit Enter.
4. Notice how the search doesn't get initiated until you now hit enter a second time. Previously that was not the case, you'd only have to hit enter once.

Thanks for reading.

Shawn

Thanks for the feedback. You can hold Shift when you click/press Enter on a one-off button to execute a search immediately. We're going note this override in the 83 release notes to make people aware of it. See bug 1671815 comment 1.

That works just fine for me, thanks for the advice.