Read Firefox Preferences Names (about:config)

[Grumpus]

Maybe there's a misunderstanding since your post indicates you wish to determine how many copies of something any user accessing your site is allowed to make.
Your methods indicate reading the users preferences and limit them by changing the preference on the users machine, this is what is improper, even if you re-instated the users preference when done. If you want to limit the number of copies you should do it on your end of the connection not internally in the users machine or system.

[supun151515]

Hi Grumpus,
Thank you for your reply. How can I limit number of print copies from server side? When the user clicks on print, it will appear print dialog. user can select how many copies from that.

[Grumpus]

This seems to be a useless quest, in order to do what you wish you have to disable the users security and change supposedly secure settings or have access to printer firmware from the manufacturer which would allow insertion of the limiting code, recognized by the firmware to ceate the on-off condition in the file to be printed. Again the system and printer would have to be left secure and back to user settings not yours.
Maybe contact a couple of the printer manufacturers.

[therube]

"coupon printers" limit copies ... http://couponsinthenews.com/2016/10/12/ ... ng-change/

[Grumpus]

@the rube - This may be good for the coupon people but it could turn out to be an enormous exploit opportunity beyond what they have to put up with already.
Where they should deal with this is on the redemption end and not in the printing end, something coded on the coupon itself, once redeemed the agent's (retailer, &c) system accepting the coupon instantly sends the information back to the source. They do this with top up and music cards. It shouldn't be on the user or their devices.
Was looking at the hows and whys of this and it seems to me you could encode the file but this in essence would be malware.
Recording the access of an identifiable individual to a site is usually normal if the have some form of login.
Changing machine settings would again be unscrupulous and unethical even if a printer manufacturer went along with it.
Printing also may have a dual meaning here and applied to a file copy format.
One of the examples of the access to hardware being applied improperly is HP printers, when on line, being sent a signal showing the printer cartridge being empty when it's not.
It locks up the system until you replace the printer cartridge. Turning it on or off, removing the cartridge and re-inserting no longer helps.
Best for some models to print offline only. This can also be an exploit due to browser functions in the printer or on the system or printer discovery outside the local network.
Anyone with a laser printer or copier knows a little shake, rattle and roll will reconstitute the cartridge, if only briefly, so HP oversteps it's rights in under the guise of being helpful.

[therube]

Anyone with a laser printer or copier knows a little shake, rattle and roll will reconstitute the cartridge, if only briefly

Likewise some judicious use of opaque tape on a "sight glass" on some cartridges (https://www.google.com/search?q=brother ... unofficial).

[supun151515]

Bytheway how can I limit print copies via firefox?

[Grumpus]

@supun151515 - It looks like no one here knows how or would be willing to tell as it would allow an exploit no one wants.

@therube - nice tip.

[kreemoweet]

Bytheway how can I limit print copies via firefox?

You can't . Firefox is an internet browser, not a device-controller, and attempting to control devices not your own is a crime.

[Grumpus]

@kreemoweet - I doubt that's a real concern to the OP.

[supun151515]

But there should be a way to limit number of print copies in web page printing