Firefox 42+ has a new Tracking Protection feature that is enabled by default in Private Browsing mode. You can see a shield icon at the left end of the location/address bar when you are in private browsing mode that some content is blocked. You can disable this feature in "Options/Preferences > Privacy".

• Options/Preferences > Privacy: "Use Tracking Protection in Private Windows"

• https://support.mozilla.org/kb/tracking-protection-firefox
• https://support.mozilla.org/kb/control-center-site-privacy-and-security-firefox

The resource at "http://connect.facebook.net/en_US/sdk.js#xfbml=1&version=v2.5" was blocked because tracking protection is enabled.[Learn More] www.urgentfiles.com
The resource at "http://www.google-analytics.com/analytics.js" was blocked because tracking protection is enabled.[Learn More] www.urgentfiles.com
The resource at "http://platform.twitter.com/widgets.js" was blocked because tracking protection is enabled.[Learn More] www.urgentfiles.com

• privacy.trackingprotection.pbmode.enabled
• privacy.trackingprotection.enabled

But if I do this it'll works only in my side so what about the viewers. How they fix this type of error ?

Is this a Firefox problem or its a JS problem which conflicts with Firefox on=load action.

You can't fix this on your website. Firefox uses a list that is maintained by a third-party website (disconnect.me). If users choose to have Tracking Protection enabled then they should be aware how it works and check for the shield icon at the left end of the location bar. This shield icon is not very noticeable, so you can easily miss it.

The about:privatebrowsing page that appears when you open a new private window shows whether TP is enabled or disabled, but permanent Private Browsing mode (Always use Private Browsing mode; never remember history) doesn't.