Goto Preference -> Tabs -> check the last one "when i open a link in a new tab switch to it immediately"

Maybe with this Add-on that adds a "Open link in current tab" to the right-click context menu - https://addons.mozilla.org/en-US/firefox/addon/open-in-current-tab/

If you are referring to using context (right-click) search with your default search bar engine after highlighting a word or phrase and having the results overwrite the current tab from which you are searching, try this extension (the instructive material on the add-on page is a bit "foggy" on whether it will open the results in the same tab and overwrite the page from which you are searching) - https://addons.mozilla.org/en-us/firefox/addon/context-search-x/

ok thx

muz_1234:

Did one of the replies above solve your question?

To indicate which reply solved your question, please click on "Solved" to the right of that reply when you are signed-in to the forum. That way, other users with a similar question, can find a solution. Thanks.

https://addons.mozilla.org/en-us/firefox/addon/selected-search/, i didnt use yours, but i managed in finding this one.