This happened with me 4-5 times. I open some website or want to do something else, but another website gets opened automatically. Yesterday, I tried to close my Firefox browser but instead of closing, it opened a website I visited few minutes before. Also, once I clicked a link on torproject.org which I clearly know where it will take me but a different website opened. Another example is I clicked my bookmark of Tor Stack Exchange website but it took me to indianexpress.com. I can confirm no malicious or new websites are opening. Just those which I previously browsed.
What could this be? A virus or malware? I already quick scanned my computer with Avast and MalwareBytes but found nothing except PUP.BundleInsaller.RKN and PUP.Optional.OpenCandy by M.Bytes but they seems legit as they were in MP3ConverterSetup.exe (from Softpedia, no virus, no spyware…) and in GOM Player respectively.