Same problem with Firefox 4.0 and 4.0.1 on Linux, flash version is 10.2.159.1-0.2.1 (latest version for openSUSE 11.4). Same problem in Konqueror Version 4.6.2 (4.6.2) "release 3".

Ugly workaround: type text somewhere else, copy or cut it, then paste (using the mouse! Ctrl+V does not work). Not sure if this workaround work on Mac.

In Opera 11.10 and Chromium 12.0.731.0 no problems entering text in the text forms.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

See also:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

If it does work in Safe-mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

• Use "Disable all add-ons" on the Safe mode start window to disable all extensions.
• Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")