To download your certificate, you must either disable your popup blocker or set it to allow on our sites.
Depending on your browser, you may see a warning, or you may have to preemptively change your settings. You might be unable to access your certificate from a tablet or smartphone. By default, Google Chrome blocks pop-ups from automatically showing up on your screen. When a pop-up is blocked, the address bar will be marked "Pop-up blocked." 
You can also choose to allow pop-ups.
- In the address bar, click "Pop-up blocked."
- Click the link for the pop-up you want to see.
- To always see pop-ups for the site, select Always allow pop-ups and redirects from [site]
Done.
If you are using Safari, you will need to do this from your preferences.
In the Safari app on your Mac, choose Safari > Preferences, then click Websites.
Click Pop-up Windows.
Allow pop-up windows for:
A website in the list: Select the website in the right column, then choose the option you want.
All websites that aren’t currently customized: Click the “When visiting other websites” pop-up menu in the bottom-right corner of the pane, then choose the option you want.
You can see all websites you’ve customized under Configured Websites. If you don’t see Configured Websites, either you haven’t customized a website yet, or you’ve cleared the list. See Change Websites preferences in Safari on Mac.