This software enables the user to add and use userscripts, which are JavaScript programs that can be used to modify web pages.

[5] In January 2019, Biniok wrote in a Google Groups post that the new Chrome manifest V3 would break the extension.

[6] On January 6, 2019, Opera banned the Tampermonkey extension from being installed through the Chrome Web Store, claiming it had been identified as malicious.

[7] Later, Bleeping Computer was able to determine that a piece of adware called Gom Player would install the Chrome Web Store version of Tampermonkey and likely utilize the extension to facilitate the injection of ads or other malicious behavior.

The site stated, "This does not mean that Tampermonkey is malicious, but rather that a malicious program is utilizing a legitimate program for bad behavior," going on to call Opera's blacklisting the extension for this reason a "strange decision".