Napping.Synth.Download4) Because your Firefox fork is still 99.999% Mozilla code contributions, you're dependent on Mozilla fixing security bugs in your browser. But you don't get those fixes when Mozilla releases them; you only get them when the fork team merges them into their fork. You have no guarantees that will happen in a timely fashion. It may never happen at all.
Follow-up points, to answer frequently asked questions:
"Are you saying I should switch to Chrome?" No. I hate Chrome. I'm just saying no current Firefox fork is the silver bullet many people seem to think it is.
"Are Firefox forks inherently doomed?" No. I could imagine a Firefox fork that was a credible alternative. It would just require a lot more resources than any existing fork has.
"What's your suggestion then?" I don't have one. The current options all come with a long list of drawbacks. You have to choose which drawbacks you can live with.
"That sucks!" Yeah man. Everything sucks these days. I don't know what to tell you
Follow-up points, to answer frequently asked questions:
"Are you saying I should switch to Chrome?" No. I hate Chrome. I'm just saying no current Firefox fork is the silver bullet many people seem to think it is.
"Are Firefox forks inherently doomed?" No. I could imagine a Firefox fork that was a credible alternative. It would just require a lot more resources than any existing fork has.