Firefox has quietly shipped one of the more practical browser AI integrations available, and most people have no idea how deep the customization goes.
The AI sidebar, which appears as a panel alongside your browsing, works by passing prompts to an AI provider's website via URL parameters. Out of the box, it connects to the major AI services. But dig into Firefox's about:config settings and you can point it at practically anything. Set browser.ml.chat.hideLocalhost to false and it accepts local models running on your machine. Set browser.ml.chat.provider to a custom URL and you can route queries to DuckDuckGo's AI chat, a self-hosted instance, or any service that accepts prompts via URL parameters.
The prompt system is where it gets genuinely useful. Firefox lets you define custom commands stored in config keys like browser.ml.chat.prompts.0 through browser.ml.chat.prompts.N, each containing JSON with an id, label, and prompt value. The prefix system supports three dynamic placeholders: %tabTitle% for the current page title, %url% for the address, and %selection% for highlighted text. These get injected automatically, so you can build one-click workflows like "summarize this selection in the context of this page" without retyping context every time.
This sits in a different lane than dedicated AI tools like ChatGPT or Claude's desktop apps. It is not trying to be a full AI workspace. Instead, it puts a context-aware AI assistant one click away while you browse, and the custom prompt system means you can tailor it to your actual workflow rather than settling for generic "summarize" and "explain" buttons. For anyone already using Firefox, it is worth five minutes in about:config to see what the sidebar can actually do.