I found this question from 5 years ago https://support.mozilla.org/en-US/questions/1097979 and it looks like the accepted answer still works today for normal releases of Firefox. e.g. this URL works: https://download.mozilla.org/?product=firefox-91.0.2-partial-91.0.1&os=win&lang=en-US&force=1 However the URL format for Firefox Developer Edition doesn't seem to accept version strings, so I can't find MARs for devedition e.g this URL works for devedition: https://download.mozilla.org/?product=firefox-devedition-latest&os=linux64&lang=en-US But these two don't (the second would be the pattern for a MAR): https://download.mozilla.org/?product=firefox-devedition-92.0b8&os=linux64&lang=en-US https://download.mozilla.org/?product=firefox-devedition-92.0b9-partial-92.0b8&os=linux64&lang=en-US Presumably MAR files are available for devedition?