Do you have firefox filter installed? I find that with my problem I disabled firefox filter from my add ons & found that the web page I have trouble viewing (which is verizon wireless) will load correctly. Or maybe is another add on you may have installed. Test them out. For now I switched back to firefox 3.6 because I dont experience that problem with 3.6. I hope they can correct it, I would like to use firefox 4 again soon.

Thanks for your reply, I also wondered if it was something to do with Firefox4 so switched back to 3.6 and low and behold my pages opened correctly. just have to see whether it happens again.

I dont think it will happen again, I switched back a few days ago & so far so good. It's definately firefox 4, when I tried to open web pages with sea monkey (which is also related to mozilla) I did not have a problem opening pages & them loading. Let's just hope it gets corrected. Best wishes!!