i'm missing some of the default search engines in the bar ebay and amazon. i hit the button "restore default search engines" in setting to try and fix it no luck. only give me back wikipedia, bing, duckduckgo but not amazon and ebay two sites i visit a lot.

this been happening to me for the past year and every time i had to go in the c drive and delete the mozilla folders and reinstall firefox to get them back. then use it after a month or two later they disappeared for no reason. this only happens on my desktop and not my laptop how do i make this stop happening?