So I clicked on a link store.bitcoin.com/ and the page didn't load, and I didn't download anything. However afterwards Avast kept popping up saying its blocked a threat: HTML;Paypal-B [Phish] with the web shield periodically when opening new tabs. I don't have this issue on Chrome and it only seems to happen on Firefox. I've tried deleting all the history, cache, and cookies to no avail. No threats pop up when I scan with Avast, Malwarebytes, or Spybot.
This is obviously very annoying and am hoping there's a fix for this.
Is there anything new in the Downloads folder? Extending the thought there, is there any new JS, COM, or EXE file that you don't recognize? Or a new extension in Firefox. Maybe a Firefox configuration setting that changed? I'm thinking here, that maybe you have a back door that's repeatedly trying to load the actual attack code. The back door might be slipping around the malware checks somehow.
If so, then perhaps uninstall FF and reinstall it.