Hello there. If you paste "about:preferences" in your browser you should be able to direct the startup, new page tab, etc. Right on the top. I'd double check to make sure that the program's "secret" installation is deleted/removed as well. Which you can check your add-ons/extensions; about:addons

As well, I'd recommend a security scan of some sort just in case of a particular long-term security threat.

HI   !

Zachary is right about checking your extensions and running malware scans, for hmyquickconverter.com is a browser hijacker   !

Go to the 3-bar menu => Addons => and look for any unfamiliar or suspicious looking extensions, like e.g.:

SafeSearch Incognito SearchAssist Incognito

When you find any :   remove them.

Also look in :   Advanced => Network tab => Under : 'Offline Web Content and User Data'

Do the same in Windows' Control Panel => Programs.

However :   most malware will be 'hiding' somewhere , so let's run malware scans :

Further information can be found in this article :
https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners.
They all work differently   -   what one program doesn't pick up, the other might.

Also see : https://malwaretips.com/blogs/remove-search-hmyquickconverter-com/