Ah, yes, you have to right-click on the page. It's not in the menu toolbar. And then you have to go into pagesync.js. Good work! I shouldn't have been so quick to blame Linux. Except it was presumably Linux's fault that Steve had to disable the sqrl:// handling in the first place :) .
And here it is: http://www.GRC.com/groups/sqrl:17932
I'll just add that Google Chrome behaves the same way. Also, as you suspect, if the SQRL client is running and listening to localhost:25519, it will run in CPS mode and present the login dialog box without needing to be invoked with the SQRL:// URL
This newsgroup posting from 2017 provides some background on the autorun feature:
As far as I can tell, the HKCU\...\Run entry was subsequently replaced with a flag bit (0x2) in the REG_DWORD "OptionSettings" at HKCU\software\gibson research\sqrl. The bit...
An earlier version of the SQRL Spec ( https://www.grc.com/sqrl/protocol.htm ) states the following:
Any OTHER server data: Due to the fact that login session-state information is being placed onto a web page where it is then taken up by an SQRL authenticator, the value of any other token the...
If you base64url-decode the last three you get
server data: (initially, the sign-in button URL)
identity signature: ( 64bytes)...
Extract from it sqrl-CLIENT-SIDE-LOGGING.exe and put it with your GRC sqrl.exe file ( probably in C:\Program Files (x86)\GRC )
If sqrl.exe is running, exit from it then from a command prompt in that directory run...
If you just run the program it creates and runs a sample SqrlVect.txt file which shows you all the types of "vectors" it can generate. I started with items on the SQRL-Client-Crypto chart and have been adding others of interest , such as the SQRL-specific base 56 encoding.