Thanks for this detailed and helpful review. Regarding point 2, I never thought of it but have just uploaded a new version 3.2 which fixes this issue. Page Hacker toolbar no longer appears on the print output.
About the positioning of the toolbar, it is actually "fixed" and should not move when you scroll the displayed page, so that you don't have to search for the toolbar. I have just tested it on mozilla.org homepage with Firefox 57 as well as the latest nightly. Isn't it what you want, or are you noticing a different behaviour on some websites?
Finally, regarding the toolbar lagging behind the cursor when moving it, this is an annoying issue that I did notice on earlier versions of Firefox but no longer since Firefox 57. Can you provide me your OS, the versions of Firefox you tested and basic specs of your computer (CPU, RAM, GPU) so that I can do some additional testing? Can you check as well that hardware acceleration is not disabled in Firefox settings ("General" panel, "Performance" section)? Feel free to send me these details here or by email at nicopensource at free dot fr.