The new version has the same malfunctions that were present in 24.7, namely when any Google sites (Search, Calendar, and especially Gmail) are open in a Firefox browser, after a brief period of minutes the sites will fail to refresh or reload, causing a yellow popup in Gmail to read "Oops, the system encountered an error..." and behaving as if the connection is offline. When this happens, the only way to get Gmail or Search or Calendar to refresh is to close out the browser and relaunch Firefox. Disabling Avast web shields immediately corrects the issue. With webshields enabled, the error keeps happening repeatedly when Gmail is left open in a Firefox tab. The issue does not happen when using a private Firefox browser, which requires the user to sign into accounts every time the browser is launched, which makes it a troublesome workaround.
Users of Avast Free and paid version on Windows 10 or earlier PC computers with Firefox have extensively reported the issue on the thread fo the previous Avast version 24.7...
https://forum.avast.com/index.php?topic=328185.0