That is the fuction of the apostrophe key: it finds words that you type that are also links. The forwardslash key does the same but for any words on the page, not just links.
However, it shouldn't happen when you're typing in a textarea (it doesn't for me or rojash by the looks of it).
Goto your start menu, and open firefox in safe mode. Then goto this site and try and post a question: still get the same issues? If not, it may be an extension that you have installed that's interfering.
If you still get the same issue, then try uninstalling and reinstalling firefox.