I meant to say in the main message I've scanned with Malwarebytes and also couldn't download Firefox from the Mozilla site using Firefox - I either got 0 bytes worth and a 'finished' download or it stalled after downloading a small portion of the file. Also having a problem downloading images from my account with depositphotos.com - they appear to download but are also 0 bytes.

Printed.com loaded instantly for me, but I'm using Linux & the latest Fx version. You appear to use Win XP? Long shot, but some sites may not support it.

List the exact steps used in when downloading the ones that fail. Some sites download can fail if: don't have cookies enable don't have java script enabled sites' server is busy / down file no longer exists; AV software is blocking some files; other reasons

Could be a lot of reasons - maybe multiple. 1. did you try starting Fx in safe mode (only disables addons).

2. did you create a new, clean profile, then try the sites? If not, close Fx. In Windows "run box" - probably under Start > Run, enter: firefox -P (in Windows, possibly firefox.exe -P) Leave space btwn firefox and '-P'. That starts the firefox profile manager.

Choose to create a new profile; name it something meaningful; Select or highlight the new profile name; Uncheck where it says ~ "use this profile every time without asking."

If it solves the issues, it indicates a problem w/ addons or plugins or "corrupted" profile.

See also this article about the Profile Manager:

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

Boot the computer in Windows Safe mode (press F8 at the startup) with network support to see if that has effect in case security software is causing problems.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

cor-el said

See also this article about the Profile Manager:

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

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Boot the computer in Windows Safe mode (press F8 at the startup) with network support to see if that has effect in case security software is causing problems.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

I'm not able to use safe mode with network support because the PC is wireless and wireless doesn't load in safe mode on this PC.

Anyway, I think this may be something to do with AVG Free anti-virus as suggested by cor-el. I was able to switch off the 'Online Shield' component of AVG and early indications are that this could be the cause of the problem. When Online Shield switched itself back on after 10 minutes, the problem with video recurred straight away.

I've posted on AVG to see if others have the issue and will repost here if I get to the bottom of it. I don't want to say AVG is defintiely the issue yet because the problem was always erratic - sometimes sites that hadn't loaded would suddenly load fine at the second or third attempt.

Thanks for the help so far, really appreciated.

Thanks to cor-el for suggesting a security software issue.

I reinstalled AVG but made no difference to problem.

I've since removed AVG and replaced it with Avira and now everything works as it should.

Thanks again to cor-el.