Reproducing instructions: 1. Define Hebrew as the interface language of your phone. 2. Install the Android GMail app. 3. Go to Menu -> More -> About. 4. Tap the "Send feedback" link. 5. Select "Nightly" in the menu that will open, to open the link in Mobile Firefox Nightly. 6. A form will appear. Scroll all the way down to the last large text area. 7. Tap in the text area. An on-screen keyboard is supposed to appear, but it doesn't. It does appear if I open the same link in the built-in Webkit browser.
(It does work in Nightly if the interface language of the phone is English.)
Amir, are you able to reproduce still on more recent versions of Firefox?
It's not relevant anymore, the app doesn't open the browser.