-> Clear Cookies & Cache

• https://support.mozilla.com/en-US/kb/Template:clearCookiesCache

-> Clear the Network Cache

-> Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

Check and tell if its working.

Thanks. I've followed your advice and (one by one) I've deleted cache and cookies, disabled add-ons and plug-ins, gone into safe mode, updated extensions and gone into default theme. None of them make any difference. Of course thye problems are resolved if I load Virgin Mail in Basic HTML, but that's not what I want to be in.

I should have added that I also tried clearing Network Cache.

-> Try the suggestions mentioned in the following articles:

• Firefox can't load websites but other browsers can
• Lower the max number of HTTP connections

Check and tell if its working.

None of those actions make any difference

Create a New Profile as a test to check if your current profile is causing the problems.

-> Basic Troubleshooting - Make a New Profile

IF that New Profile works then you can recover your Bookmarks and Passwords from the Old Profile.

-> Recover important data from an old profile

Check and tell if its working.

Thanks, that probably would fix it but I don't want to tamper with my profile in case I make a mistake and mess things up. Thanks anyhow.