However, Tristan Nitot, president of Mozilla Europe, told ZDNet UK on Thursday that Firefox 4 would not have the option, which is technologically difficult to implement.
"We have been investigating [the option], but so far we haven't found a way of combining a 'do not track' option with a good user experience," Nitot said.
Nitot said there is a good chance that web pages would not load properly if a user has the blocker enabled. The multiplicity of sites that track user behaviour, added to the number of ways users can be tracked, means that blocking user tracking can break web pages.
A Mozilla spokeswoman told ZDNet UK on Thursday that the privacy option was just one approach and not a 'comprehensive solution' for privacy on the web.
"We have been working with other organisations to discuss ways to design the right solution, and there is more work to do. Firefox 4 will not ship with what we envision is the end-to-end solution; we don't think any browser can today," the company said in a statement. "Mozilla has always believed that users should have control over their web experience, including who has access to information about them and on what terms."
The company said that there is no easy fix to online privacy, and that any product would need to be a "simple, verifiable and complete" way to give web users control.
"[Do not track] will need to work for the two billion people on the web today and will require collaboration across the entire ecosystem, from users to web developers and anyone interested in creating an open and participatory way for users to control their web experience," the spokeswoman added. "And once defined, we will ship that solution as part of Firefox."
The privacy mechanism has support from US regulators. On 1 December the FTC issued a report (PDF) supporting a 'do not track' option for site users.