AdwCleaner found these delta files, but I have checked FireFox and there is no sign of Delta Search anywhere in that programme. I looked in FF extensions and addons, no mention of Delta.
File : C:\Users\Ric\AppData\Roaming\Mozilla\Firefox\Profiles\40ih0slm.default\prefs.js
Found : user_pref("extensions.delta.admin", false);
Found : user_pref("extensions.delta.aflt", "babsst");
Found : user_pref("extensions.delta.appId", "{C26644C4-2A12-4CA6-8F2E-0EDE6CF018F3}");
Found : user_pref("extensions.delta.autoRvrt", "false");
Found : user_pref("extensions.delta.dfltLng", "en");
Found : user_pref("extensions.delta.excTlbr", false);
Found : user_pref("extensions.delta.ffxUnstlRst", true);
Found : user_pref("extensions.delta.id", "b8457168000000000000ac7289c7aa52");
Found : user_pref("extensions.delta.instlDay", "15865");
Found : user_pref("extensions.delta.instlRef", "sst");
Found : user_pref("extensions.delta.newTab", false);
Found : user_pref("extensions.delta.prdct", "delta");
Found : user_pref("extensions.delta.prtnrId", "delta");
Found : user_pref("extensions.delta.rvrt", "false");
Found : user_pref("extensions.delta.smplGrp", "none");
Found : user_pref("extensions.delta.tlbrId", "base");
Found : user_pref("extensions.delta.tlbrSrchUrl", "");
Found : user_pref("extensions.delta.vrsn", "1.8.21.5");
Found : user_pref("extensions.delta.vrsnTs", "1.8.21.519:23:31");
Found : user_pref("extensions.delta.vrsni", "1.8.21.5");
Found : user_pref("extensions.delta_i.babExt", "");
Found : user_pref("extensions.delta_i.babTrack", "affID=121240");
Found : user_pref("extensions.delta_i.srcExt", "ss");
It found other stuff like 'Babylon' but I have no idea which files are suspicious or harmless so I haven't opted for delete.