Unfortunately I can see from the Huawei M835 specifications that it has armv6 which is an architecture that is not supported by Firefox. Only android devices with armv 7 and greater can install Firefox Mobile. Any way I don't see that your device is not compatible here : https://wiki.mozilla.org/Mobile/Platforms/Android so maybe you can try to download manually the build and install the apk. Find builds here: http://ftp.mozilla.org/pub/mozilla.org/mobile/