If you can enable installing from 'Unknown sources' try http://ftp.mozilla.org/pub/mobile/releases/latest-beta/android-r7/en-US/fennec-4.0b5-en-US.eabi-arm.apk

Thank you sir.

However, it downloaded ok (after insisting on having another mozilla.org between pub & mobile), but only produces the useful message 'Application not installed'. I'm going to look at the logs, & try an adb install, but that will have to wait till the morning :)

Finally got back to this

adb install fennec-4.0b5-en-US.eabi-arm.apk

1195 KB/s (12344982 bytes in 10.085s)

       pkg: /data/local/tmp/fennec-4.0b5-en-US.eabi-arm.apk

Failure [INSTALL_FAILED_INVALID_APK]

Eh !

You can also try the nightly builds from here: https://wiki.mozilla.org/Mobile/Platforms/Android

Thanks gentlemen.

Update.

I've upgraded from 2.1 to 2.2, this has included an app called Toshiba Market, which appears to be very similar to the Google market. This Market has Firefox 4 available, though it does have an identity crisis, not knowing whether it's 4-1.0b2 (apk) or 4.0b2 (running), which installed & runs.

It does have some issues, but since these are not related to download or install, I'll raise another topic if required.