When the same issue affects multiple browsers, an extension is less likely to be an issue, but... it would still make sense to test in Firefox's Safe Mode just in case. That's a standard diagnostic tool to bypass interference by extensions (and some custom settings). More info: Diagnose Firefox issues using Troubleshoot Mode.

You can restart Firefox in Safe Mode using

Help > Restart with Add-ons Disabled

In the dialog, click "Start in Safe Mode" (not Reset)

Any difference?

By the way, the avast! Online Security extension has been implicated in some other site rendering issues, so if that one is cross-browser, I'd definitely try disabling it.

Hello Jscher - thank you for your suggestions. I have tried both but no better, unfortunately best Vince

Is there anything special about the way you connect to websites? For example, do you use any private VPN or similar service, anonymizing proxy, TOR, etc.?

Hello jscher

thank you for your help, but not really - I use plus-net ips with wired connection to the router. Occasionally I use startpage search engine which has the option of connecting with proxy server. But I don't use that to normally connet to web pages.

I attach a screenshot from this link

http://www.bbc.co.uk/iplayer/episode/.../Bargain_Hunt_Series_29_Kingston_15/
so that you can see what I mean with it looks strange.  I have also made sure that java script is enabled

best rgards Vince

Many of the style sheets load from a different server:

<link rel="stylesheet" type="text/css" href="http://static.bbci.co.uk/frameworks/barlesque/2.58.1/desktop/3.5/style/main.css"  /> 
<link rel="stylesheet" type="text/css" href="http://static.bbci.co.uk/iplayer/3.68.1/style/episode/utilities.css"  /> 
<link rel="stylesheet" type="text/css" href="http://static.bbci.co.uk/bbcdotcom/0.3.212/style/3pt_ads.css"  /> 
<link rel="stylesheet" type="text/css" href="http://static.bbci.co.uk/iplayer/3.68.1/style/iplayer-min/global_iplayer.css"  /> 
<link rel="stylesheet" type="text/css" href="http://static.bbci.co.uk/iplayer/3.68.1/style/drawers/drawers.css"  /> 
<link rel="stylesheet" type="text/css" href="http://static.bbci.co.uk/iplayer/3.68.1/style/episode/episode.css"  /> 
<link rel="stylesheet" type="text/css" href="http://static.bbci.co.uk/iplayer/3.68.1/style/drawers/overlays.css"  />

When such "third party" content does not load, it may be caused by filtering the requests in some manner. This could be as simple as blocking third party cookies, or something more complex. In another thread, we could not find any way for a user to have his Firefox fetch the third party content without first visiting a link on the other server directly.

Could you check your cookie setting? This article describes that section of the Options: Websites say cookies are blocked - Unblock them.

If that doesn't help, try visiting one of the above links (they are just pages of style rules) and then return to the page and see whether that makes a difference.

Hello Jscher

Thank you sooo much! I realise now what happened: I have blocked all websites that start with "static." to avoid to be taken automatically to spywaresites like http://static[dot]australianbrewingcompany[dot]com and http://static[dot]salesresourcepartners[dot]com

law of unintended consequences and so very kind that you have helped me. and it's fixed now. (except for the spyware) Vince

regarding the malware, run a full scan of your system with security tools like the free version of malwarebytes & adwcleaner. other users reported that these programs could catch & remove this malware...

Troubleshoot Firefox issues caused by malware

Hello philipp thank you for your advice - I have made a start on this now

kind regards Vince