Since you've installed Firefox 4.0 you can sign up to the Youtube HTML5 trial which you'll find at HTML5 Trial

All you need to do is to click the link at the foot of the page; there's no forms to fill in or anything. YT is in the process of converting its whole dbase to the new format.

If you still can't view a certain type of video, could you please provide a sample link to one or two of them please.

Thanks for taking the time to respond. I signed up for the trial although I wasn't prompted to download anything, should I have been? I still can't open videos and as they aren't showing any properties I can't put in the link.

All you have to do to sign up to the trial is click the link (nothing to download).

To provide a link even if you can't open the video, right click it and choose Copy Link Location. This will copy it to the Windows Clipboard.

Then come here and either hit CTRL+V, or right click and choose Paste from the menu.

The howto videos are displayed in a column on the left hand side of the screen. Right clicking does nothing but I do get the link text at the bottom, here are a couple of examples:- http://www.wonderhowto.com/how-to-browse-websites-without-mouse-287379/ http://www.wonderhowto.com/how-to-speed-up-firefox-page-display-time-218595/ If I type the links in the address bar it will take me to the videos which I can then open but this is laborious as I have to write the links out first since they disappear when the mouse arrow moves off the video show down the left hand side. Hope this makes sense to you.

Can you try running Firefox in Diagnose Firefox issues using Troubleshoot Mode? If you can do what you can't do now in that configuration, then one of your add-ons is the culprit.

No good since the how-to videos are an add on feature so can't test.

OK, if I understand you correctly now, you're talking about this Add-on How To Videos Sidebar

That being the case, use the email support option which you'll find on the right hand side of that page (where it says "Need help with this add-on?")

I'll try that right away, thanks. Sorry for wasting your time, I'll try and be more explicit with future problems, lesson learnt.

No problem. Could you please click the "Helpful" button? This will mark the thread as "Solved".

If you don't get any joy with the developer support, you can post to the dedicated Add-ons forum @ Mozilla Add-ons Forum in the AMO Feedback section.