In `~/.config/mimeapps.list` you need to add
```
x-scheme-handler/http=google-chrome.desktop
x-scheme-handler/https=google-chrome.desktop
```
to ensure the default browser (Google Chrome in this case) is invoked
when running `xdg-open https://pt2.allsup.co/`.

So my `mimeapps.list` file looks like
```
[Default Applications]
text/html=google-chrome.desktop
x-scheme-handler/http=google-chrome.desktop
x-scheme-handler/https=google-chrome.desktop
```