The Ubuntu file browser does not show hidden files and folders by default. Here is the look of file browser when browsing the root file system normally:

As seen all of the hidden/system folders are not seen. If you want to see hidden file just hit Ctrl+H at the screen, you will immediately see all the hidden files:

If you would prefer to make this be the default setting when using file browse then go to the Edit menu and select Preferences:

Check the “Show hidden and backup files” checkbox and now you will see the hidden files all of the time.