AdBlock Plus has successfully defended itself in court for the second time in five weeks.
The service prevents ads from appearing on websites unless it has given them permission to be displayed.
German broadcasters RTL and ProSiebenSat.1 had argued that browser plug-in was anti-competitive and threatened their ability to offer users content for "free".
However, a court in Munich ruled in favour of AdBlock's owner Eyeo.
Ben Williams, a spokesman for the German company, told the BBC the dispute had been the biggest one it had faced to date "just by nature of the people involved and the amount of claims that they had".
"This is the fourth time that massive publishers have brought legal proceedings against our start-up," he added in a follow-up email.
"Thankfully, the court sided with users and with compromise. So, we're pleased to say that Adblock Plus will continue to provide users with a tool that helps them control their internet experience.
"At the same time we will endeavour to work with publishers, advertisers and content creators to encourage non-intrusive ads, discover new ways to make ads better and press forward to a more sustainable internet ecosystem."
A spokeswoman for RTL responded: "We are weighing a possible course of action against the ruling and assessing the prospects of an appeal."
Last month Eyeo successfully defended itself against similar claims by two other German publishers - Die Zeit and Handelsblatt - at a court in Hamburg.
It still faces a further case brought by another local publisher, Axel Springer, in Cologne.
Eyeo offers its Adblock software to the public without charge, but makes money by operating a "white list" of adverts that it allows to get through its filters.
Such ads must meet certain criteria. For instance they must not include animations or sounds and cannot be pop-ups that cover other content.
Website operators that want ads on their site added to the white list must seek permission.
Although Eyeo states that "no one can buy their way" onto Adblock Plus' list, it does charge fees for what it terms "support services", the details of which are not made public.
The firm says its PC browser plug-in has been downloaded about 400 million times.
It also recently released a version for Android-powered devices that it says has been downloaded more than 220,000 times, and it promises an iOS version soon.
However, as part of its ruling the court in Munich said that too few people were using Eyeo's products for it to be judged to have a "dominant" position that might justify an antitrust intervention.
Adblock Plus is not the only tool threatening the business model of sites that provide free content and make money from selling their readers' "eyeballs" to advertisers.
Mozilla is also promoting the optional Tracking Protection feature for its Firefox browser, which stops many internet cookies from being downloaded.
This limits the ability of affected sites to show personalised adverts, which are worth more money to them.
Earlier this week, one of the organisation's former employees published a paper suggesting that use of the tool sped up page load times by about 44%. She called on the organisation to switch the setting on by default.
"The internet's principal revenue model leads to misaligned incentives between users, advertisers, and content providers, essentially creating a race to the bottom," Monica Chew wrote.
"Industry wields the most political and economic power, so it is up to users and user agents to advocate for the interests of people."