Adobe's Flash software is now blocked by default on all versions of the Firefox web browser.
Mozilla, which develops Firefox, imposed the block because the recently unearthed bugs in Flash were being actively used by cyber-thieves. On its support pages, Mozilla said the block would remain until "Adobe releases an updated version to address known critical security issues".
Attackers were known to use vulnerabilities in Flash to install malicious software on computers and steal data. Adobe said it was planning bug fixes.
Mozilla also gave advice about how to adjust Firefox's settings so Flash would only run with the permission of a browser's user rather than all the time. It said users should only activate Flash on sites they trust. Firefox is the third most popular desktop browsing program, according to figures gathered by analysis firms that monitor browser market share.
The block comes soon after Facebook's newly appointed security chief Alex Stamos publicly called for Adobe to kill off Flash. "It is time for Adobe to announce the end-of-life date for Flash and to ask the browsers to set kill-bits on the same day," he said in a tweet.
Flash, and other Adobe products, regularly feature among the top 10 applications favored by criminals keen to compromise computers and steal saleable data because they are used on so many devices.
Adobe has already moved to close one of the vulnerabilities. However, it said it was still working on patches for two other bugs. It said patches for the other bugs should be available later this week.