Clear the cache and the cookies from sites that cause problems.

"Clear the Cache":

• Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now"

"Remove Cookies" from sites causing problems:

• Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

when i want to open it , after a while it says : is taking too long to respond and when it is loading , if i press stop button , i cant reload it again in fact the reload button turns off before i ask this question , i deleted all my cache and cookies the most interesting thing is that all the people can load it but me and of course i can load any website but it please help

Did you try Safe-mode?

• Help > Restart with Add-ons Disabled

• http://kb.mozillazine.org/Error_loading_websites
• https://support.mozilla.com/kb/Error+loading+web+sites

You can try to reset (power off/on) the router.