Why is the QQ browser not the default browser but when you open the Web page or the default boot?

Because of the need for browser compatibility test installed a QQ browser, I set Firefox as the default browser, but each time you open the connection is the start of the QQ browser.

There are two possible scenarios in which this can occur:
1, the cancellation of QQ for the default browser open settings are unsuccessful, if you need to cancel QQ as the default browser can be done as follows. Tools →tt options → comprehensive settings → default browser, then select the browser you want to set as your favorite;

2, through the QQ client click the main menu → system settings → security and privacy → security → the "use of QQ browser to open the link in QQ, enhance the security of access network" before the tick removed.

In this way, the link opened in QQ is opened by our default browser.

Why is the QQ browser not the default browser but when you open the Web page or the default boot?