This has been bothering me for a while, but with the start of a new semester and working on many different machines, it's been happening a lot more frequently. Let me explain: Problem: My homepage for a new window will seemingly at random change to a file in `file:///usr/share/doc/HTML/index.html` despite my profile having a setting for `browser.startup.homepage` to be `about:home`. Expected Behavior: I set my homepage to `about:home` and this is respected by the system and does not change. After some digging, I've tracked down the cause (but not the issue) Steps to reproduce: 1) On my linux desktop (Rocky Linux 8.5 -- a RHEL clone; KDE; Firefox 91.13) I set `browser.startup.homepage` to be `about:home` 2) On a Windows machine (I'm not 100% certain if I can replicate with other non-Windows systems) open firefox and login to my firefox account and run a sync. 3) Back on my linux box, when I open a new window, the homepage has changed to no longer be `about:home`. What seems to be happening is that a sync will simply delete the `browser.startup.homepage` preference line entirely from the `prefs.js` file for my profile. On the Windows machines (I have not checked macs, or ubuntu boxes I use), the "default" homepage setting (i.e., what happens when the `browser.startup.homepage` line is deleted from the prefs.js file) goes to `about:home`. On my Rocky Linux box, the "default" setting seems to be inheriting the homepage from a file named `all-redhat.js`. Or at least, I think that's where this comes from. My temporary solution is to: > In about:config try toggling the preference services.sync.prefs.sync.browser.startup.homepage to false on the laptop / desktop devices. (from: https://support.mozilla.org/bm/questions/1273715 ) I'm guessing this will work for now. However, my actual question is to track down how these default settings are coming from! On the linux box, in the directory `/usr/lib64/firefox/defaults/` I have `pref/channel-prefs.js` and `preferences/all-redhat.js`. There is no `mozilla.cfg` or really any way I see that `all-redhat.js` is loaded. The `all-redhat.js` file does have a pref setting for the `browser.startup.homepage` to set it to be `data:text/plain,browser.startup.homepage=file:///usr/share/doc/HTML/index.html`. The windows boxes are a little different in that they do have a mozilla.cfg that gets explicitly loaded and in the mozilla.cfg sets a homepage in a similar way. However, the behavior, as described above, is different. The `about:home` seems to be a default, despite the homepage setting in mozilla.cfg. What I'd like to know is: What is the loading priority of these config files, and how is the best way to setup a system that behaves consistently across OSes? While syncing works great for the most part, trying to understand the mechanics of the preference/profile loading is really making me scratch my head! Does redhat (and its clones) just do things differently?