using trickle to slow down browser

Solution 1:

I think the confusion stems from your comprehension of the man page. ncftp is the name of the process being limited, so to limit firefox you would do:

trickle -u 10 -d 20 firefox

Solution 2:

The "error" you're getting is more of a warning/notice than an error. trickle can be run standalone or as a client of trickled. It always looks for the default socket of the daemon and if not found it prints that message. You can safely ignore it.

And about rate limiting Firefox, I'm pretty sure it has to do with the forking of the process, as David Fraser mentioned. You can also see a warning about it in Arch's Wiki, where it says:

Warning: Trickle can only limit traffic of programs that do not fork, so shaping a FTP server's traffic won't really work that way!

In my own experience, I've tried to limit aws-cli tool for S3 upload unsuccessfully, but have been able to limit s3cmd instead. Both tools are written in python, but aws-cli are many different programs bundled through a main one while s3cmd is a single program. I'm guessing the same issue with forking is happening there.

So my short answer is: I don't think you can rate limit those browsers using trickle.