I use Xpra on Debian 10 to view an application in the HTML5 client. I build the Debian package for the LTS version 3.0.10 from source. The most recent revision doesn't work for me, the HTML client keeps restarting. (xpra v3.0.10-r26457)
I can recreate the bug with the command:
xpra start --bind-tcp=0.0.0.0:8888 --start=gedit
And logging in through Firefox on the localhost.
The problem seems to be introduced with this commit that uses guess_content_type: r26327
reverting the change fixes the problem for me.
I haven't tested the official builds and don't know if it is just my build.
Thanks for reporting this bug. As you found out, the backport was faulty, r26459 fixes that.
FYI: 3.0.10 has not been released yet.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2775