Mozilla is ending Firefox support for the Amazon Fire TV platform and Echo Show devices starting on April 30th. The browser will stop receiving security updates after that date, and you'll no longer be able to install it either. Of course, that also means you won't be able to reinstall it if you decide to remove it from your device or if you perform a factory reset to start from scratch.
Amazon gave Fire TV and Show owners access to Firefox in 2017 shortly after Google announced that it's blocking the YouTube app on the devices. It rolled out availability to Silk, its own browser, before that, but it also launched Firefox to give users another option and to "to make it easy for [them] to access the Web from the comfort of their couch." As it turned out, Amazon added Firefox support just in time, because Fire TV users lost access to the YouTube app earlier than expected.
The browsers allowed users to stream videos from the Google-owned platform on their devices even while the tech giants weren't in good terms. At the time, Googled explained that its decision was borne out of the "lack of reciprocity." A spokesperson explained: "Amazon doesn't carry Google products like Chromecast and Google Home, doesn't make Prime Video available for Google Cast users, and last month stopped selling some of Nest's latest products."
After the tech giants made up, Amazon reinstated YouTube support on the Fire TV, which means users no longer need a browser to play its videos. As Android Police notes, though, the Echo Show doesn't have a dedicated YouTube app yet, so owners will have to rely on Amazon's Silk browser.