FG Joomla to WordPress

First verify your login and password to the Joomla database.
If Joomla and WordPress are not installed on the same host:
If you use CPanel on the Joomla server, a solution is to allow a remote MySQL connection.

go into the Cpanel of the Joomla server
go down to Database section and click "Remote MySQL"
There you can add an access host (WordPress host). Enter the access host as the SOME-WEBSITE-DOMAIN-OR-IP-ADDRESS and click add host.

Another solution is to copy the Joomla database on the WordPress database:

export the Joomla database to a SQL file (with phpMyAdmin for example)
import this SQL file on the same database as WordPress
run the migration by using WordPress database credentials (host, user, password, database) instead of the Joomla ones in the plugin settings.

I get this error when testing the connection: "SQLSTATE[HY000] [2002] Connection refused" or "SQLSTATE[HY000] [2002] No such file or directory"

This error happens when the host is set like localhost:/tmp/mysql5d.sock
Instead, you must set the host to be localhost;unix_socket=/tmp/mysql5d.sock

The migration stops and I get the message: "Fatal error: Allowed memory size of XXXXXX bytes exhausted" or I get the message: “Internal server error"

First, deactivate all the WordPress plugins except the ones used for the migration
You can run the migration again. It will continue where it stopped.
You can add: define('WP_MEMORY_LIMIT', '512M'); in your wp-config.php file to increase the memory allowed by WordPress
You can also increase the memory limit in php.ini if you have write access to this file (ie: memory_limit = 1G). See the increase memory limit procedure.

I get a blank screen and the import seems to be stopped

Same as above

The media are not imported

Check the URL field that you filled in the plugin settings. It must be your Joomla home page URL and must start with http://

The media are not imported and I get the error message: "Warning: copy() [function.copy]: URL file-access is disabled in the server configuration"

The PHP directive "Allow URL fopen" must be turned on in php.ini to copy the medias. If your remote host doesn't allow this directive, you will have to do the migration on localhost.

Nothing is imported at all

Check your Joomla version. The Joomla 1.0 database has got a different structure from the other versions of Joomla. Importing Joomla 1.0 database is a Premium feature.

The posts put in trash are not migrated. But unpublished and archived posts are migrated as drafts.
Some users reported that the Zend Framework causes an incomplete import. So, if all the data is not migrated, consider deactivating the Zend Framework during the migration.

I get the message: "Fatal error: Class 'PDO' not found"

PDO and PDO_MySQL libraries are needed. You must enable them in php.ini on the WordPress host.
Or on Ubuntu:
sudo php5enmod pdo
sudo service apache2 reload

I get this error: PHP Fatal error: Undefined class constant 'MYSQL_ATTR_INIT_COMMAND'

You have to enable PDO_MySQL in php.ini on the WordPress host. That means uncomment the line extension=pdo_mysql.so in php.ini

No, it only reads the Joomla database.

I get this error: Erreur !: SQLSTATE[HY000] [1193] Unknown system variable 'NAMES'

It comes from MySQL 4.0. It will work if you move your database to MySQL 5.0 before running the migration.

I get this error "Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM"

You must use at least PHP 5.3 on your WordPress site.

I get this error: SQLSTATE[HY000] [2054] The server requested authentication method unknown to the client

It is a compatibility issue with your version of MySQL.
You can read this post to fix it: http://forumsarchive.laravel.io/viewtopic.php?id=8667

None image get transferred into the WordPress uploads folder. I'm using Xampp on Windows.

Xampp puts the htdocs in the applications folder which is write protected. You need to move the htdocs to a writeable folder.

You can use the Convert Post Types plugin after the migration.

No, you can deactivate or even uninstall the plugin after the migration (for the free version only).

Yes since version 1.45.0. First you must put these lines in wp-config.php:
define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
And the messages will be logged to wp-content/debug.log.

The plugin imports the Joomla web links to WordPress links managed by the Link Manager plugin: https://wordpress.org/plugins/link-manager/

My screen hangs because of a lot of errors in the log window

You can stop the log auto-refresh by unselecting the log auto-refresh checkbox