10ten Japanese Reader (Rikaichamp)

Quickly look up Japanese words on any text page by activating the add-on from the toolbar or pressing Alt+R.

Features:
• Pitch accent information
• Dictionaries that update automatically twice a week
• Recognition of a wide range of grammatical forms and characters (e.g. 食べてた,  分からん, 知らん, じーちゃん, 頑張ろー, そーゆー, ぬ verbs, とく・どく forms, causative passive, vs-c verbs like 兼した, and characters like ㋕, ㌀, ㋿, 𠏹沢, and many more)
• Translation of Japanese numbers into Arabic numerals (e.g. 13億5千万 into 1,350,000,000)
• Translation of yen amounts (e.g. 100億円, 8万8千円) into a local currency
• Translation of Japanese-era years into Gregorian years (e.g. 昭和５６年, 平成三十一年)
• Translation between 畳/帖 measurements and square meters (e.g. 四畳半、12.6 帖、25 平米 etc.)
• Translation of shogi moves (e.g. ☗８三銀引成)
• Support for the widest range of Web content (Google docs, YouTube subtitles, vertical text, SVG images, hidden text etc.)
• Support for non-English dictionaries (unfortunately no Japanese-Japanese dictionary is freely available yet)
• Up-to-date kanji data including educational and kanji kentei levels, reworked kanji components etc.
• Many settings to customize to your needs
• Localization into Simplified Chinese and Japanese
• Automatic preview of name entries when there is a better match in the name dictionary