Mimer since its newest version calls actually harbour-webcat --set-default when it detects harbour-webcat being chosen. So harbour-webcat --set-default should work just fine in setting the correct default browser. The terminal output however shows Setting as default first and then comes the usual warnings that you get apparently when loading qml stuff from c++ in SailfishOS nowadays. And then it exits. I tested on Jolla, Jolla C, Jolla Tablet and my Xperia X aswell as the Moto X2 port and it is working fine there. I even tested it on my Gemini PDA right now and it is working there fine from Mimer.
That sounds like a broken dbus service. The way how it works is that the default browser is set to a dbus service that either calls the openUrl function of the already running browser or when the browser is not running execute a command to start it. This should work just fine when harbour-webcat --set-default does its magic of setting the default browser (actually copying over the dbus service file and using it as default). I found maybe a bug in mimer which might set the webbrowser after harbour-webcat --set-default is running which might lead to an issue. So maybe you need to manually run harbour-webcat --set-default after setting it as default in mimer. I will take a look at that when I have more time dealing with it.
You can swap it. Last time upgrading worked fine. But I cannot guarantee it.
Maybe it was a split second the sensors told it to be in landscape and it started loading landscape UI and then switched to portrait which took a second as it was loading all the components it needs in the background
I had that and removed it and no one cared :P Tripple click is confusing as hell from a user perspective. I am currently out of ideas when it comes to how this can be implemented in any sane way currently without feeling awkward. Honestly I don't see an issue with the two clicks that we have right now.