The simplest solution would be to change the User-Agent string that identifies your browser to one that the store will accept as bona-fide Firefox.
To override this string :
- Type about:config into Firefox’s address bar and press Enter
- Type
general.useragent.overridepreference
in the search box, and if it exists go to step 4 (double-click it) - Right-click on the
about:config
page, point toNew
, and selectString
- Name the preference
general.useragent.override
- Enter your desired user agent as the value of the preference.
A searchable database of user-agent strings can be found in myip.ms, where you can search for one that suits you.
Another (tiring) solution would be to google for the addon and then download the xpi file.