For Firefox, setting the "dom.event.clipboardevents.enabled" about:config option to false prevents clipboard paste events from reaching javascript. No more blocked pasting after you toggle that option, even if the website attempts to do so.
Use "Paste" from right click menu. Configure your environment to use a different paste keyboard combo. Use the old X11 clipboard with middle button paste.
For Firefox, setting the "dom.event.clipboardevents.enabled" about:config option to false prevents clipboard paste events from reaching javascript. No more blocked pasting after you toggle that option, even if the website attempts to do so.