Firefox does not work in macOS Dock
Greetings. I've seen some similar questions about Firefox and the macOS Dock, but I think I'm seeing something different. I'm using macOS 10.12.6 and Firefox 60.0.1 (after upgrading from 58.something today in an attempt to fix this issue). So, starting from Firefox closed and not on the dock, here's what happens:
If I drag Firefox to the dock from the Applications folder and click on the icon I just dragged there (henceforth the "old" icon), a new Firefox icon appears over on the right end of the dock with a running-program dot below it. The old icon just sits there unchanged. If I exit Firefox, the new icon disappears and the old one stays, still unchanged. If I tell the Dock to keep the new Firefox icon, the new icon will work for relaunching Firefox for 10 seconds or so, after that clicking on the new icon will give a question mark over the icon and Firefox will not launch. If I relaunch Firefox from the old icon, the question-marked one stays unchanged and I get another new Firefox icon.
This behavior has been consistent over the last few months, and is not changed by upgrading Firefox or by deleting it from the Applications folder and reinstalling. None of my other applications do this, it's apparently unique to Firefox. It's workable, but it's weird and annoying and I'd like to be able to fix it.
First, please update to Firefox 61.0.1. The version you are running is old.
Second, can your computer run Mac high Sierra? I'd suggest updating to that.
Then, please try not dragging Firefox to the dock first, just open it, then pin. Does it stay?
My apologies, a typo on my part--I'm on Firefox 61.0.1. I typed 60.0.1 by mistake.
High Sierra - I think I could update, but my experience in the past is that updating macOS is more likely to break something than fix something. I don't view updating macOS as a reasonable approach to fixing any particular problem since I assume that, whether it fixes that particular problem or not, it will probably create some other, unforeseen, problems. Every upgrade implies 5-10 hours of download, install, and troubleshooting whatever breaks. So... I don't do it unless I've got a full day to devote to just that.
Pinning rather than dragging--I get the same behavior minus the "old icon" described above. So, if I launch Firefox without dragging it to the dock first, I get a Firefox icon over on the right of the dock. If I just quit Firefox at that point, the icon disappears, which is what it's supposed to do. If I go to "Options --> Keep in Dock" on the right-click popup, then quit Firefox, I've got about a 10 second window in which I can reopen Firefox from that pinned icon, and after that clicking on it just gives a question mark over the icon with no launch of Firefox. I can't reopen Firefox at that point without going to the Applications folder and launching it from there. Basically, a dragged icon has partial functionality in the dock, a pinned icon loses all functionality shortly after closing Firefox.
Now that I think about it more, I think upgrading macOS to 10.12 probably coincided with this odd functionality of Firefox in the Dock. So... could upgrading again solve it? Maybe, but I might reasonably conclude upgrading is how I get this kind of problem, right? If doing X breaks Y, don't do X...
You should always run the latest version of your OS, for security and stability reasons. I'd suggest updating your OS (It shouldn't cause any issues). If that doesn't fix the problem, https://support.apple.com/en-us/HT201639 might help.