Perspective addon Noté 5 sur 5 étoiles
This addon is good if you have few search engines. But if you have 40-50 engines to open all searches in tabs becomes ridiculous.
But it is possible to add this ability with not so big efforts.
The options should allow to choose some subset of search engines and assign this subset to some profile (name). It will be like folders, but allow overlaping. So, the "Search using" item in context menu will list the profiles names, and each profile - its search engines. One of such profiles (main profile) will show its search engines on upper level, i.e. together with profiles. Moreover, such organization will not require "Open all searches in tabs" - clicking on profile name will do this
Regarding "Organize search engines" - this addon a little bit conflicts with omnibar addon, when you want to use urlbar also for searches - it doesn't allow to change the default search engine..