There's a *lot* of packages that make up MicroB (microb-engine, tablet-browser-daemon, tablet-browser-ui, ...) so reinstalling that is rather unfeasible...

Have you tried moving the Mozilla settings folder? Try "mv /home/user/.mozilla /home/user/.mozilla.old" (not as root). If that doesn't do anything, just run "mv /home/user/.mozilla.old /home/user/.mozilla". If it does change something, you're gonna have to search the folder properly for references to that font