Same here, I've tested Opera and Firefox. I haven't bothered trying other browsers because if it doesn't work with Firefox, the most popular browser, it may be considered broken.
But I can branch out alright...
I hadn't noticed the "edit" link, which is under "more". I'll try that then.
I can't reply directly to you below (which could become above one day, I suppose, if you are voted up over me (EDIT: Ah the new mapleprimes now offers the ability to rank messages by date instead of by votes, that's GREAT!), so I'll reply as an edit.
On another thread where I was unable to post yesterday, I was suddenly able to post a reply today, but unable to post further afterwards; one reply seems to have been my quota.
No luck on this thread at all so far.
I mostly use Opera. Firefox behaviour is similar. I'll now try Chrome and Internet Explorer out of curiosity (I don't have Safari on hand).