http://flashvd.net/.well-known/http-opportunistic opens to a JSON web page.

When/how often does this happen? When the browser is closed?

What were you doing at the time? surfing, watching a clip, reading something . . . .

It happens every 15 minutes (only if firefox is running, not with other browsers). I do not recall what I was doing the first time it happened, but I'm pretty sure I was doing nothing out of the ordinary. (opened the usual web sites, the ones I am opening daily since years. no strange downloads, no click on unwanted links).

Start Firefox using Troubleshoot(Safe) Mode {web link}

A small dialog should appear. Click Start In Troubleshoot(Safe) Mode (not Refresh). Is the problem still there?

You may have ad/mal-ware. Further information can be found in this article; https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed free to use malware scanners. Each works differently. If one program misses something, another may pick it up.

The problem it is not showing while in safe mode. I am running some of the anti-malware... but nothing has been picked up yet...

Hi wimrada,

Try Refreshing your Browser:-

• To do this, click the menu button at the top right corner of the Firefox window.

• Click the “Help” option near the bottom of the menu.

• Click the “Troubleshooting Information” option in the Help menu.

• Click the “Refresh Firefox” button at the top right corner of the Troubleshooting Information page.

• You’ll be warned that this will remove your browser add-ons, reset your customizations, and revert other browser data to the default settings. Click “Refresh Firefox” to confirm you want to make these changes.

The problem it is not showing while in safe mode.

It could be the work of one of your add-ons,

Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; <Control> (Mac=<Command>) <Shift> A)

In the Add-ons Manager, on the left, select Extensions. Disable a few add-ons, then Restart Firefox.

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All Of them.

If the problem continues, disable some more (restarting FF). Continue until the problem is gone. After, you know what group is causing the issue. Re-enable the last group ONE AT A TIME (restarting FF) until the problem returns.

Once you think you found the problem, disable that and re-enable all the others, then restart again. Let us know who the suspect is, detective.

The culprit add-on seems to be: Flash Video Downloader (http://www.fvdmedia.com/). The strange part is: I have it installed since more than 2 years (and the last update was 1 year ago) and never had any issue. Maybe the issue was always there but Sophos is picking it up just recently and not before? Anyway, now I know how to get rid off that annoying recursive message. Thank you very much :)

That was very good work. Well Done.