$20 for a browser extension that blurs text on a page! Yikes! This strikes me as the sort of generic productivity tool that might be worth a buck or two, but for $20, it had better blur text AND file my taxes for me. I would be really surprised if there were not free extensions that did effectively the same thing. And if there are not, someone could probably whip it up in a day or two, and there goes your business.
Pricing is incredibly hard to get right. It's very, very likely that the market for a tool like this is small, so charging $2 would actually net the author far less than charging fewer people $20. In that regard it's correctly priced at $20. The apparent simplicity of some code has absolutely no impact whatsoever on the amount you should charge for it. What you charge for your product should be based on the value tha…
Go one level deeper. How much effort would a competitor have to put into building a competing product and undercutting you?
If the answer is "one afternoon," then you either need to figure out a way to make competition less likely or set a more realistic price.