@josefano09

If the issue persists in just one browser, I'd be less likely to think it's a permissions issue -- instead, I'd be on the side saying it's an issue with WordPress or one of the plugins you've installed. Still, it never hurts to check file and directory permissions just to be sure.

Login to the CLI as your root or sudo user and navigate to the directory where the site is located. From there, you can use ls -al to view the user:group that currently owns each file and directory.

When it comes to stock installations of Apache using mod_php (which is what most use), the files and directories need to be owned by the same user that Apache is running as. In most cases, that's the www-data user unless you've changed it or it was previously set to something else. If you have a different setup, use the user you know works.

From there, you should be able to simply use chown to recursively change the user:group owner. If the current file or directory is already owned by that user, nothing will change. If a file or directory isn't owned by that user:group, then it will be after the command is ran.

So if WordPress is installed to /home/user/public/, we can run:

chown -R www-data:www-data /home/user/public/*

I wrote about the problem and a temp fix in my blog:
The upload is not working in WordPress media uploader