Just a simple question. I want to install a deb package and which should I select - 32bit or 64bit package? My ubuntu is 64bit version, but recently I read for some programs they advice to install 32bit packages, so now I am confused.
Let's say Mozilla only makes Firefox available as 32-bit software - if you are using a 64-bit version of Adobe Flash Player, it will be incompatible with Firefox because 64-bit software is only compatible with 64-bit software (32-bit software is compatible with both)...
But if you had both the 32-bit and 64-bit version of Flash Player installed, you'd have the 32-bit version for Firefox (in addition to any other Flash-enabled/powered 32-bit software), and the 64-bit version for any 64-bit, Flash-enabled/powered software you are running.
As a rule-of-thumb, you should always try to get a hold of 64-bit software where possible as it offers better security, more stability and in most cases, better performance (the Ubuntu Software Center will usually try to install 64-bit versions of software, where available, if your computer is already configured as a 64-bit system)... Which in part is tied to the higher memory (RAM) allowances supported by 64-bit software.
It's when you start talking about extensions/plug-ins/etc that 32-bit software might be the way to go... But often these are available in 32-bit and 64-bit varieties, so just install both if you use a combination of 32-bit and 64-bit software (or just stick to 64-bit software!).
By the way, it is the 64-bit version of Firefox that installed by default under a 64-bit Ubuntu operating system... Just in case you were wondering. ;-)