I have a preference named "browser.search.defaultenginename" but I do not have one named "browser.search.defaultengine".

If you repeat the experiment, adding the search box and then removing it again, does it reset again? I'm not noticing any change to a manually set "browser.search.defaultenginename" when I do that.

Hai jscher2000, Thanks for the reply

I changed my default search engine for address bar searching using 'about:config -> Keyword.Url' . Which changes my address bar based search to this default search engine. (like this https://support.mozilla.org/en-US/questions/756322) - Please refer attached picture for the current status which doesnt work.

And as mentioned in my problem, when i remove the search toolbar from the ribbon i see that the keyword based search which was fine before (select word-> right click-> Search X for "...") is now (select word->right click-> Search Google for ".."). Let me know if i am missing something here, does changing the name matter ("browser.search.defaultenginename")?

There does seem to be an effect. Based on some clicking and dragging, this is what I see:

Search box displayed: right-click menu item uses "browser.search.selectedEngine" (same as search box)

Search box NOT displayed: right-click menu item uses "browser.search.defaultenginename"

Does it work to set "browser.search.defaultenginename" to the preferred value?

yes it works when set to the preferred value. Solution found, but strange that this happens. Thanks