What file or setting holds default browser info now?

All, After installing opera and brave, both installed at the default browser. Easy enough to fix with Firefox->Settings->Set as default, but that prompted a question -- where is that information stored? How do browsers know where to look -- and where is that? In the past it was a setting in kcontrol->KDE Components - but it is somewhere else now. Anybody know? -- David C. Rankin, J.D.,P.E.