I'm using Firefox 34 on Debian testing / KDE and DD-WRT site works fine. Applying settings can have different effects. Some require router reboot apparently, some not. In the former case it can disconnect. I don't think it's a browser problem though.
You often see cautions about cache related/induced issues.
I generally find that with frequent cache flushes I can get along, so am primarily looking for alternatives that folks find 'better', which I understand can be a moving target.