https://support.apple.com/guide/mac-help/look-up-words-mchl3983326c/mac
This is a feature I have dearly missed since migrating from Chrome. Currently it is only accessible through ctrl + cmd +d or using three-finger click.
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Some similar ideas here:
Word meaning shown in pop up window like safari
Define word function
Need this so bad. Love Firefox on macOS, but it really needs the native look up feature. Chrome has it, Firefox should too.
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