So far the only issue I’ve had switching to 64-bit from 32-bit Ubuntu has been Flash. In some Flash content, mouse clicks are not recognized. Everything looks correct, but any left clicks are ignored. Most notably, the problem affects YouTube videos. Here’s the Ubuntu bug report.
A 64-bit browser can not load 32-bit plugins. On 64-bit systems, this is worked around using a plugin viewer called nspluginwrapper that can load 32-bit plugins. The bug seems to be caused by an interaction between some changes to GTK, nspluginwrapper, and Adobe’s Flash Player. Adobe needs to update their plugin to fix the problem.
I’m using Ubuntu 10.04 64-bit with Flash Player installed from the flashplayer-installer package (via Ubuntu Restricted Extras). The following workarounds worked for me:
Workaround 1: disable desktop effects. Open System->Preferences->Appearance and select the Visual Effects tab. Select None to turn off desktop effects. The issue should be immediately resolved.
Workaround 2: tell GTK to use its old behavior for the Flash Player. If you don’t want to lose desktop effects, this is probably the solution you’re looking for. Press Alt-F2 to open the Run Application dialog and paste the following command:
gksu gedit /usr/lib/nspluginwrapper/i386/linux/npviewer
You will be prompted for your password so you can edit the configuration file. Add this line as the second to last line in the file:
The file should look like this when you are done:
You will need to refresh the page with Flash content for this fix to take effect.
Both workarounds work on my system in Firefox and Chrome. As a last resort, you can also try installing Adobe’s pre-release (and possibly buggy) Flash Player for 64-bit, but I have not tried this myself.