User Agent: Mozilla/5.0 (Android; Mobile; rv:24.0) Gecko/24.0 Firefox/24.0 (Nightly/Aurora) Build ID: 20130812172216 Steps to reproduce: Open a form like this one (Mozilla "Enter A Bug" page. Copy some short text. Put the cursor in a field ("What Did You Do?") Long-press the text area/field. Tap "Paste". Actual results: Nothing. Expected results: Text is inserted into the form field.
Works for me on Nightly (08/15) using my LG Nexus 4 (Android 4.3). Can you try out Nightly for Android and report back if that works out for you? (http://nightly.mozilla.org). Also, which device and Android OS are you testing with?
It turns out it was an OS problem, not a Firefox problem. Upgrading Android (from a highly unofficial build) fixed it. Thanks!