I know the smart quote conversion website, dan hersam.com, corrects the problem but
most people don't use it.
I am certain that site is using regex (Regular Expressions) to parse the text and do the real time fix. It would be easy to mirror their approach and just do it real time while posting. Regex is extremely efficient. It would not slow FR down hardly at all. Milliseconds per post. Regex kicks out assembler level efficiency looking at text. You can check it out yourself. Google Grep and install the software. Try searching your entire hard drive without indexes etc and compare it to Windows or Mac searches. It is BLAZINGLY fast. (Grep uses regex)