Don't forget to habitually select all text then ctl c before clicking 'post reply'
For quite a while now, using the Back command in FireFox worked when I forgot to copy before posting and I mostly use it as my workaround now.
The trick there is knowing to put the tab in the background, ignore it for a while, check recent posts to see if you actually posted even though you got a Boom message, and then try posting again if it looks like your Boom wasn't one of the ones that invites double posts.