I went through some of the other posts, and dowloaded FRST, Malwarebytes Anti-Malware and Malware Anti-Rootkit tools.
The anti-malware tool found the following problems:
Proceeded with cleaning it, and no other threats were found by any of the tools. Also refreshed Firefox, after disabling extras that I knew were malware.
However, I still get the annoying pop-up ads almost always whenever I open Firefox (sometimes it doesn't happen but it's rare) and sometimes it hijacks the homepage as well, instead of just showing the malware as pop-up ads.
These are the most recent logs from Anti-Malware and FRST:
Scan Log 2.txt
Some terms are in Portuguese, but I hope you can understand them.