If you have the focus in the address bar and press Tab, Firefox puts you into search mode (while retaining focus in the address bar) using your default search engine. Is there something missing?
So that doesn't work.
I also don't want to search my default search engine. I want tab to search for the panoply of websites that the omnibox will search. When I start typing ebay, I want "tab to search ebay".
I know I can set them up manually (a pain, but might be worth the investment to avoid the google overlord), however, I still don't get the "tab to search blah" function with a keyword. I have to type the keyword exactly -instead of having tab function as autocomplete- then space for my query.
What I want is omnibox tab to search.
You can configure Firefox to do this with a single checkbox. Go to Settings, click Privacy & Security on the side, go down to the Address Bar section, and make sure that "Search engines" is selected.
When I do that, I can click in the address bar (which brings up the drop-down), type "ebay", and then you'll see "Search with eBay" appear below in the drop-down, and then a single Tab puts it into eBay search mode.