Seems more useful than Chromes search bar which has tab-to-go-to-google-search-and-generate-ad-revenue. At least Firefox has down-to-find-what-I-actually-want-from-my-bookmarks-and-history.
No.
If I type eba{Tab}query, firefox should search ebay for query. If I have to go to settings once and tick a box to enable this functionality, I will. I won't stop wanting what I want.
2. Find an eBay search engine you like, install it in Firefox.
Now, when you type eba{Tab} Firefox will suggest the search engine you installed, and your continued typing will be as a search in that engine.
I don't use this for eBay, but I do use it for Rust, typing e.g. rust{tab}iterator takes me to the documentation for std::iterator and related entries.