Well, you can always remove libflashplayer.so but there is more of an elegant solution - in MicroB go to Options / Add-ons, click on the Plugins tab, click on Shockwave Flash and then on the Disable button next to it. The change should be immediate if nothing with Flash content is opened in the background, but if it doesn't stick, right after disabling the plugin jump to xterm and reset the browser stack by hand: