You don't need any add-on because Firefox already has the capability to search for tabs for years (since at least 2012).
Many people know that typing in the address bar will give you various suggestions including your currently open tabs, but few people know that you can specifically tell Firefox to search only opened tabs with
%. So just press Ctrl+L, Alt+D or F6 then type
% to search
If you have a lot of tabs then there's another way to search them by clicking the tab overflow button > Search Tabs
Mozilla is Making it Easier to Search Open Tabs in Firefox
Similarly you can search in history and bookmark with and
* respectively just like
Changing results on the fly
If you are looking for a specific type of result, like a bookmark or tag, you can speed up the process of finding it by typing in special characters after each search term in the address bar separated by spaces:
^ to search for matches in your browsing history.
* to search for matches in your bookmarks.
+ to search for matches in pages you've tagged.
% to search for matches in your currently open tabs.
# to search for matches in page titles.
$ to search for matches in web addresses (URLs).
? to search for matches in suggestions.
Besides, Firefox has always had the option to switch to the most recently used tab and show a preview on Ctrl+Tab instead of the next tab in order