Firefox used to be a great browser and it still has some great features, I still use it as my second browser choice as I like some of the plugins and features... But about 10 years ago they started to have huge memory leaks and those huge memory leaks still plague the browser today making it unstable if left open for extended periods of time or with multiple tabs open... It's a shame they have been unable to plug the leaks and stabilize it, and now that they announced they are severing ties with Google who has been their primary bank roller for 10 years, I fear things might get worse...
Chrome isn't perfect (it has it's own share of memory leaks) but it's more stable then Firefox...
I could never get Safari to run properly on a Windows computer without crashing regularly, probably part of the reason Apple gave up on the Windows version several years ago...
And on that topic that might be part of the problem you are having getting rid of the Trojan as the last Windows release of Safari was in 2012 and it no longer supported, thus the malware scanners might not be supporting it either...