palemoon

Pale Moon is a free and open-source web browser licensed under the MPL-2.0 with an emphasis on customization. Its motto is "Your browser, Your way." There are official releases for Microsoft Windows, FreeBSD, macOS, and Linux.
Pale Moon originated as a fork of Firefox, but has subsequently diverged. The main differences are the user interface, add-on support, and running in single-process mode. Pale Moon retains the user interface of Firefox from versions 4 to 28 and supports legacy Firefox add-ons.

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