I don't know if it is related, but after I upgraded Firefox it was having all sorts of problems. Most obvious, if I opened a new blank tab and then entered a URL, it would never load the page. But clicking on a link and choosing open in new tab would work find (and I could then type an unrelated url and it loaded fine).
I ended up uninstalling Firefox and wiping the profile from the hard disk and then re-installing. Suddenly everything worked fine. I'm assuming it didn't handle some upgrade to the config/profile properly.
I haven't actually tried to use tiddlywiki with the latest Firefox yet, so it may not be related.