Proxy Activation

1. Open browser

2. Download FoxyProxy extension

3. Create proxy using FoxyProxy extension (Options > Add):

4. Add it:

   
5. Save.

6. Open Burp Suite.

7. Set the interceptor on (Proxy > Intercept > Intercept is on):

1. Go to browser and activate the proxy created with FoxyProxy:

2. 
3. Finally, reload the page you want to intercept, and its source request will appear in Burp Suite.