The singer-songwriter took the stage in Toronto Thursday night and -- as she does at all her concerts -- she performed a mashup of 2 popular tracks ... both breakup songs all about Joe this time around.

Watch the clip ... Taylor sings a medley of "Mr. Perfectly Fine" from Fearless "(Taylor’s Version)," and "Better Than Revenge" from "Speak Now" -- songs about her messy split from Jonas.

Swift teased in the footage, "Time for a little revenge" ... and, the vid shows her belting out lyrics like "“She came along, got him alone, and let’s hear the applause / She took him faster than you can say ‘sabotage'" -- a reference many fans think is to Camilla Belle, who Jonas started dating shortly after dumping Taylor via phone call.

If you don't know ... Taylor and Joe dated for a few months back in 2008 before Jonas called things off in a 30-second call.

While she's never confirmed "Mr. Perfectly Fine" or "Better Than Revenge" are about Joe, Swifties are sure the tracks are about the DNCE frontman.

While Taylor seemingly revealed in recent years that she's cool with Jonas -- sending gifts to him and Sophie Turner after they had their first child together -- his recent divorce from Turner may have soured the pop star on him again.

TMZ broke the story ... Sophie and Joe recently finalized their divorce after about a year of proceedings. After Joe filed for divorce, Sophie left their shared home -- and, with nowhere to go, Taylor reportedly offered her a place to stay.

BTW ... even if Taylor didn't create the mashup as a shot at Joe, many fans are taking it that way anyway -- just read the X comments. Fans are living for the drama.