Bittercrash, my experience with the «Send to Gmail» feature on the Google Toolbar for Firefox leads me to believe that the reason you are seeing this 502 error message when attempting to use the above to forward a link with Gmail might possibly be that you have configured your Gmail settings to always use https for your browser connexion. If, indeed, that is the case, try setting your browser connexion to «Do not always use https» and see if that resolves the problem. I do hope the Gmail developers will get around to fixing this bug as soon as possible....
Henri
Thanks for the tip. But https was already turned off. I also altered it in the bookmarklet code to http, but no change.