Safari constantly crashing on my iMac 2011 OS 10.12.6

I certainly have the Trusteer Rapport installed on my iPhone 12 Pro, but on my iMac only the .ipa of that app appears. The only thing I could blame for those crashes is movie downloading processes, but this has never been a problem before. the only thing that has been problematic is some bug that permanently and aggressively opens new Tabs to MacKeeper. I also have installed the Disk Doctor Pro to get rid of some garbage and put some order.

Thanks for your suggestion den.thed but I understand that there are certain features that are not well installed from the High Sierra on my iMac 2011. If you would be so kind to provide me with a Link that ensures its full functionality, I would appreciate it very much.

Edu.

Thank you all very much for your suggestions. As you can understand, I will have to do several tests to determine the functionality of each suggestion, so I will report its usefulness and result.

Thanks for your suggestions Hercules, I have implemented all of them and I am waiting for results. I will have to try FireFox to investigate...