Chromium Bridge vs Firefox Devtools MCP

browser_page_text

Get a tab's title, URL, and visible text (up to 80 kB) from the live DOM. Read-only and cheap — prefer it over a screenshot whenever layout does not matter. Content rendered to canvas or images is invisible to it; use a browser_computer screenshot for those.

browser_computer

Mouse, keyboard, and screenshots in a browser tab via the DevTools protocol; the tab does not need to be active (first use shows Chrome's "started debugging" info bar — that is expected). Actions: screenshot (viewport image in CSS pixels — its coordinates map 1:1 to click coordinates), zoom (magnified region [x0,y0,x1,y1]), left_click, right_click, double_click, triple_click, hover, left_click_drag (start_coordinate→coordinate), type (insert text at the current focus), key (space-separated combos, e.g. "cmd+a Backspace"), scroll (scroll_direction+scroll_amount), scroll_to (ref), wait (duration, max 10 s). Clicks, typing, and key presses are real input events and mutate page state; screenshot/zoom/hover/wait are read-only. Positions come from coordinate:[x,y] or from a ref returned by browser_read_page/browser_find — refs are more reliable than eyeballed coordinates.

browser_read_page

Accessibility tree of the page with a ref id per element; use refs with browser_computer (clicks, scroll_to) and browser_form_input. filter=interactive returns only clickable/editable elements — a compact map of the page. Read-only. Refs go stale after navigation or heavy DOM changes; call again to refresh.

browser_find

Find elements by visible text, accessible name, or role, and return their refs for use with browser_computer and browser_form_input. Read-only. Cheaper than reading the whole accessibility tree when you know what you are looking for. An empty result means nothing matched — not an error.

browser_form_input

Set a form control's value directly in the DOM: input/textarea/contenteditable (text), select (option value or label), checkbox/radio ("true"/"false"). Fires input/change events so frameworks pick the value up. Mutating. Target by CSS selector or ref. Reliable for plain form fields; rich editors (CodeMirror and the like) and custom comboboxes often ignore it — for those, click the field with browser_computer and type.

browser_click

Click an element via DOM .click() by CSS selector. Mutating. Works without the debugger — including on pages where CDP attach fails — but only fires the click handler, with no hover/focus/mousedown chain. If the page ignores it (custom dropdowns, canvas UI), use browser_computer left_click for a real mouse event.

browser_upload_file

Put local files into an <input type="file"> selected by CSS selector, as if the user picked them in the file dialog (fires change). Mutating. files are absolute paths on the user's machine; the input must already exist in the DOM.