If you feel this violates the guidelines of Chrome and Firefox I would suggest that you let them know by reporting the add-on which can be found here -

You can search this to see if you have been targeted https://masstagger.com/user/username and replace the username with yours

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Isn't this promoting division rather than unity? Widely, yes, I do think so. What I don't believe is that that's neccesarily a bad thing. My primary goal with this tagger is to tag users of hate subreddits. I.e. the kind of users that cannot be reasoned or compromised with. These users are known to intentionally troll other subreddits, posing as innocuous members who agree, but just have some concerns about the way you're presenting yourself. This is known as concern trolling. Ultimately, the goal of these concern trolls is to water down the message of the community into a less effective message, in order to weaken their position. By identifying those who are engaging in bad faith, we save time for those who may otherwise engage the bad actors in their concern trolling.

"Isn't this eerily similar to gold-starring Jews before the holocaust?

I've had people make that connection before. However, until I start genociding people I've tagged, or they are discriminated against by a government entity, that comparison isn't really valid. Additionally, participation in certain subs is entirely voluntary. No user is forced to post in a hate sub.

https://masstagger.com is the website and the user is u / morpen (intentionally broken to avoid the notification to them). The user history shows they are intentionally targeting subreddits and abusing the Reddit API in violation of the TOS.