Mozilla has lost some good people due to burnout. I suspect working for Mozilla carries greater risk of burnout that working for "normal" organizations. A lot of people are motivated to work for Mozilla because of our mission. This motivation is powerful and persists through unhappiness. Thus, people drive themselves to work hard at the expense of their happiness and mental health. This is a recipe for burnout.
That is very true for me. There have been long periods of time when I have been frustrated with my work, feeling I would be happier doing some other work, and in fact feeling that I'm struggling to cope. But I've survived in this job a long time, I don't currently have those feelings, and in fact I feel pretty good even though I'm currently going through some travel madness. Here's a few things that have helped.
Acknowledging the ebb and flow. When I'm feeling burned out, I slack off. I think that is OK as long as it's temporary --- and as long as I'm not using it as an excuse to be lazy. For me, it's natural to have periods of time when I'm energized, followed by periods when I'm tired and I need to back off while I rest and rekindle my enthusiasm. Per my earlier post, this is not a sign I need to change jobs.
A sense of perspective. When I feel my job sucks, it's important to take a step back and think about what I'm comparing it to. Objectively, my worst weeks at Mozilla have been worldly bliss compared to most weeks of most people over most of human history. It is critically important to never lose sight of this fact. (There are a few Mozilla people for whom this is not true; you know who you are and I tip my hat to you.) Whenever I feel like a heroic martyr, it's simply ridiculous.
Changing focus. When I'm sick and tired of working on something, it's very helpful to work on something different --- "a change is as good as a rest" (which is mostly but not entirely true). Mozilla does a lot of important things and there are a lot of very different ways to contribute to Mozilla's mission, so it's not a problem to rotate people in and out of particular roles.
Family. My wife and children are a vital anchor for my mental health. My commitments to them --- and their policing of those commitments --- prevent me from going too far overboard with work. Spending time with them, giving and receiving love, is the best tonic I have.
The Sabbath. I often struggle to rest and relax because I feel burdened with work projects and guilty for not working; this contributes to burnout. I find that compulsory downtime, decreed and ideally enforced by an external source, is extremely helpful in dealing with that guilt: I don't need to feel guilty about not working when someone is making me do it. My family is one source of that compulsion, and my Christian convictions about not working on Sunday (not always observed :-( ) are another.
Relinquish responsibility. Feelings of being irreplaceable can be extremely draining and contribute to guilt, anxiety and the difficulty of resting. Therefore it's very important to break those feelings --- forcing oneself to step aside, at least temporarily, and see what happens. It's usually not as bad as you think. We also need to keep in mind that we are only responsible for what we do; as individuals we are not responsible for Mozilla's ultimate success or failure. We have to let go and not worry about what we, as individuals or as a group, do not control. Over the years I've developed a little bit of apathy, which has been valuable.
Remember the mission. Sometimes, when enthusiasm fails, I must ask myself whether there's any work I could be doing that's more important than my work at Mozilla. So far, the honest answer has always been no, and so I know what I must do. As I suggested above, this can be a scourge, but it can also be liberating. There's a certain exhilaration in knowing what one should do, and throwing yourself into it with nothing but grim determination.
Jesus. Sorry to my irreligious readers, but this true and important. Many times I have felt myself to be running on empty, and my only recourse has been to pray to the Lord for strength to do what I know I should do. Many of those times I have been quickly refreshed in a way that feels miraculous. Apart from that immediate relief, my identity in Christ provides logical and emotional support to many of the items above: my commitment to my family, my sense of duty, my sense of perspective, my sense that God is ultimately in control, and the obligation to periodically disengage from work. Had I not been a Christian, I don't think I would have survived.