V9 is the first Firefox version that uses the new "manifest V3 "(MV3) extension API. This new format has some benefits but it also it forces us to do some things more complicated internally, thus the slower replay speed. It is the same issue that we had with Chrome and Edge when we updated the extension from MV2 to MV3
Having said this, performance improvements are on our todo list for some of the next upgrades. If you encounter a certain command that is especially slow, please let us know and we can then prioritize working on this command.
Already now you can increase the replay speed by using store | NODISPLAY | !replayspeed. It hides the GUI updates and makes the macro replay much faster. You can also use it only for some parts of the macro, and then switch back to the normal FAST mode for other parts.