If you want a browser extension to craft and store your own ChatGPT prompts, Prompt Genie is a good choice. The tool lets you create an unlimited number of prompts, save your best ones and use them through a Chrome Extension without needing an API key. It costs $6.99 per month with a 7-day free trial, so it's relatively affordable and easy to get started.
Another option is QuickyAI, which converts any webpage into a ChatGPT interface so you can use custom prompts right on the page. It works with major browsers and GPT-4 models, and has features like one-click content summarization. The extension requires an OpenAI API key, but it offers two pricing tiers, so it's a good option for productivity boosts.