Unable to add attachment to email using gmail/Firefox

[Lepros]

I recently installed Linux Lite and I have been trying it out but have had a problem with it that I haven't had with my Windows machine.

When I open gmail in Firefox, create a new email, and click on the button to add an attachment, nothing happens.

I don't have this problem on my Windows machine and I don't have the problem even on my Linux Lite machine if I use Chrome.

Does anyone have any ideas on how to solve this?

Thanks!