Welcome to Yomitan!

Here are some basics to get started

Clicking the Yomitan button in the browser bar will open the quick-actions popup.
The cog button will open the Settings page.
The magnifying glass button will open the Search page, enabling text and terms to be looked up using the installed dictionaries. This can even be used in offline mode!
The question mark button will open the Information page, which has some helpful information and links about Yomitan.
Yomitan requires one or more dictionaries to be installed in order to look up terms, kanji, and other information. Several downloadable dictionaries can be found on the Yomitan homepage, allowing you to choose the dictionaries most relevant for you. Dictionaries can be configured using the button below, or later from the the Settings page.
Install or remove dictionaries…
You can also import an exported collection of dictionaries to migrate from a different device or browser from the Backup section of the Settings page.

If you are migrating from Yomichan, you may be particularly interested in migrating your data from Yomichan into Yomitan. Please follow instructions from Yomitan's README for that.
After dictionaries have been installed, webpage text can be scanned by moving the cursor while holding a modifier key. The default key is Shift, which can be disabled or configured below.
Clicking the speaker button of an entry in the search results will play an audio clip of a term's pronunciation using an online dictionary, if available.
Clicking on a kanji character in a term's definition will show additional information about that character. (Requires a kanji dictionary to be installed.)
This startup notification can be turned off using the options below, or later from the Settings page.

Recommended Permissions (Important)

Enable recommended permissions
This will allow Yomitan to scan text from most sites. Further configuration is available on the Permissions page.

Basic customization

Show this welcome guide on browser startup
Scan modifier key
Hold a key while moving the cursor to scan text.
Scan using middle mouse button
Hold the middle mouse button while moving the cursor to scan text.
Auto-hide search popup
When no definitions are found after scanning text, the popup will be hidden.
Scan delay (in milliseconds)
Change the delay before scanning occurs when no modifier key is required.
Theme
Adjust the style of the popup.
More customization options are available on the Settings page