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https://www.waterfox.com/support/find-and-install-add-ons-add-features-to-waterfox/

Find and install add-ons to add features to Waterfox - Waterfox Support

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https://www.waterfox.net/support/android/add-ons-waterfox-android/

Find and install add-ons in Waterfox for Android | Waterfox

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https://www.waterfox.com/support/unable-install-add-ons-extensions-or-themes/

Unable to install add-ons (extensions or themes) - Waterfox Support

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https://support.mozilla.org/en-US/questions/1558872

Add-ons disabled or fail to install on Legacy Firefox (56) | Firefox Support Forum | Mozilla Support

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