I’ve been looking for a way to perform clicks in multiple tabs for a long time until @YoGo showed up and demonstrated the Broadcast Channel API 
Inspired by this I went and made a more general purpose script. For now it supports submitting edits on MB pages that end with “/edit” or “add-cover-art” and added support for MagicISRC.
However I recommend using this on the beta version only for the time being since it has better rate limit handling
You can use the multi tab submission feature either from your userscript manager’s context menu or bookmarklets:
MusicBrainz: Submit Edit (All Tabs)
javascript:(function(){ new BroadcastChannel('mb_edit_channel').postMessage('submit-edit'); })();
MagicISRC: Submit ISRCs (All Tabs)
javascript:(function(){ new BroadcastChannel('magicisrc_submit_channel').postMessage('submit-isrcs'); })();
Don’t forget to also install the auto login script for ISRC importers whose security I’ve since tightened