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How can I remove a hijacker from my browser?
In general, if you have to ask, you can't.
That is, there might be anti-malware products such as those mentioned by ToddN2000 that could do it. We don't know how any "hijacking" was done on a system you have, so we don't know how it might be undone. There are many possible hooks that can give various forms of control over a browser. Without investigation, we can't know what methods were used. So, we can't tell you how to do it.
Because you asked, it implies that you don't have sufficient background to search out methods of hijacking. If you had enough background, you'd know how to search and how to understand articles that you found.
So, you really only have two choices. You can download and run various anti-malware programs and hope one of them recognizes and fixes whatever particular problem you have. Or you can take your system to have a qualified technician look it over and, hopefully, fix the problem.
There is a third choice, but it probably takes too long. You can begin taking courses that give you the necessary background. Then you won't have to ask.
It's possibly unfortunate, but that's the way things go. I'd say to try Malwarebytes first. It'll work for you, or it won't. After that, you'll simply need to have someone fix it for you.
A corrupted file can cause your PC to be faulty, so it might help to check, delete if you can, I have Management Software that alerts me, checks for any corrupted files and asks if I would like it deleted.