We want to modify Urlbar one-offs so they filter Urlbar results to a particular engine and allow the user to continue typing, instead of searching immediately.

Will it be possible to revert/configure this though settings UI in easy way that will also work in the future updates?

I think that how on-off searches should behave should be configurable because not all users would use them (or want to use them) the same:

1. Some users already know what they are searchig for so they don't need specific suggestions for specific engine. With old way, they just need to type query and click on one-off icon. With new way, they need to type query, click one-off icon and again click on their query or press enter, so search actually triggers. This means one more click which can be inconvenient.
2. But some other users may not know what exactly they are searching for. For them, new change might be better.

(In reply to Filip Š from comment #1)

Will it be possible to revert/configure this though settings UI in easy way that will also work in the future updates?

I think that how on-off searches should behave should be configurable because not all users would use them (or want to use them) the same:

1. Some users already know what they are searchig for so they don't need specific suggestions for specific engine. With old way, they just need to type query and click on one-off icon. With new way, they need to type query, click one-off icon and again click on their query or press enter, so search actually triggers. This means one more click which can be inconvenient.
2. But some other users may not know what exactly they are searching for. For them, new change might be better.

I created bug 1671815 for this. Feel free to repeat your comment over there!

All the dependencies are resolved, closing this.