Just for a test (and not for a final solution), please go to avast main GUI -> web shield -> EXPERT settings -> "...well known browsers only". Then save the change, test and report back. PLEASE REPORT BACK.
Please also add in your next post, what AV you used to have before avast, and how you uninstalled it. Have you ran the specific removal utility for that old AV after you ran its uninstallation?