1. Type 'about:support' in the address bar.
2. Scroll down to 'Application basics' Table, and look for 'Profile Folder' in that table.
3. Click the 'Open Folder' button beside it, or copy the address into your file explorer.
4. You are now in your profile directory!

Important - If you have multiple profiles, the procedure *might* be different. I don't use multiple profiles, so I don't know anything about how that works, sorry.