This is the very irritating issue for the beginners.This is not an error actually.This is one of the most common wordpress errors.
How This Issue Comes..?
This issue comes due to mismatch of WordPress Address URL and Site URL.Initially WordPress will setup with either http://example.com or http://www.example.com.This issue comes when you install redirection plugins to set SEO friendly URLs.Those plugins may change the default URLs of WordPress Address URL and Site URL.This issue displays the following shown message on Firefox browser.
1.With Access Of Admin Area:
Login to your website admin dashboard.Then Goto Settings>>General,click on General option.Now you will get a page as shown below.
There you can find WordPress Address and Sire Address options.Make sure that both the URLs are same.This URLs are depends on your host provider normally.After making both URLs same,once check your website,it will be fixed.Now you are done.You can make both URLs either with or without prefix of “www”,this is fully depends on your host provider.
Let us go with without accessing of WordPress admin dashboard.
2.Without Access of Admin Panel:
You can do the same step as above mentioned by logging into your control panel using FTP.Goto wp-config.php file and edit it .See the following line of code wp-config.php file.
Change the both URLs to the same.Do same process as said in step1.
Definitely your error will be fixed.If still you are not fixed this issue then contact your hosting provider.
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