Of course they are cumbersome, because they are not intended to be used except in exceedingly rare circumstances. The present a number of basically Linux only setting or very advanced setting that should never really be edited. If you are not getting links to work. Start by checking your operating system has a default browser set. Then go and have a look in settings at the helper applications. If there is anything there about HTML or HTM documents delete it. If it is not fixed at that point, uninstall your antivirus and see if things get better. (BTW it is usually the antivirus, some addon it injected into Thunderbird or it's firewall component that is the issue, not Thunderbird.) When folk work out it is not a Thunderbird issue at all the quietly say no more and we never hear from them again. If they spend time fixing the antivirus or just remove it. I really don't know.