AB has been working fine for me (with Firefox) for the past couple of hours. However that's probably because I've not the MALWARE(!!!!) on my computer that appears to have found it's way onto yours!!!
Download, install and run the free version of Malwarebytes:
https://www.malwarebytes.org/free/
Points to note:
1. When installing, take care to deselect the option to install free trial of the 'PRO' version ;
2. When running it, use the 'Quick scan' option ;
3. Don't be surprised when that 'quick' scan takes over half an hour to finish ;
4. When it does so, click the button to view the results, ensure that there's a tick alongside everything listed and then click the button to delete what's been found.