Perform the suggestions mentioned in the following article:

• Firefox can't load websites but other browsers can

Check and tell if its working.

-> Update All your Firefox Plugins

• https://www.mozilla.org/en-US/plugincheck/
• When Downloading Plugins Update setup files, Remove Checkmark from Downloading other Optional Softwares with your Plugins (e.g. Toolbars, McAfee, Google Chrome, etc.)
• Restart Firefox

In the above link that mha007 gave you first see Firefox cannot load certain websites.

thank you

Thank for help so far but still not able to get onto one or two sites, this also happens in Safari as well as Firefox

PJ

Can you write-down the website addresses of websites on which you are having problems ??

• Firefox and other browsers can't load websites

Sites are www.Ebay.co.uk and www.showcuesystems.com. Please note this is only on my home Mac my works mac and Home Laptop PC are working fine , so do you think it might be a Mac problem?

-> click Firefox button and click Options -> Privacy panel -> History section -> under Firefox will: select "Use Custom Settings for History"

• Remove Checkmark from Always use Private Browsing mode
• place Checkmarks on
  1. Accept Cookies from sites
  2. Accept Third-party Cookies -> under Keep Until : select They Expire -> Now click Exceptions button and click Remove button for all entries which have Status set to other than Allow
• Click OK on Options window -> Restart Firefox

Check and tell if its working.

Sorry, Still no difference made by following your suggestion PJ

Perform the suggestions mentioned in the following articles:

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

Check and tell if its working.