You should still change your anti-virus . I am recommending you Avira because it is free, but I am using Bit Defender. Just do a full scan and wait for the results. Please reply to this post if you are still having problems.
Giedriu_M's guide is the best solution to get rid of the problem .
Browse To save is adware. It will not be sorted out with Adblock, but you can remove it with anti-malware/adware programs or by uninstalling it.
Try running Adwcleaner or use this uninstall guide for B2S
The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information.
Note: This will cause you to lose any Extensions, Open websites, and some Preferences.
To Reset Firefox do the following:
Go to Firefox > Help > Troubleshooting Information.
Click the "Reset Firefox" button.
Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
Firefox will open with all factory defaults applied.