I just installed Online Armor Free to test it out again. It works fine but tremendously slows down boot time unless you completely disable it and then go into services and disable the Online Armor helper service. Then turn OA back on or better yet, reboot. With that disabled, bootup returns to normal and the program still functions perfectly. Slow bootup is a known problem in all versions of Online Armor, especially on XP. I found the workaround in their forums and it was posted about two years ago. For some reason, they have never fixed the problem.
It also seems to be a problem if you have the Chrome browser installed.
I use OA Free and I don't have any of those problems. As far as browsers go IE,FF or Chrome makes no difference. I also noticed you refered to XP, I have a Win7 64 bit. I have absolutely no slow down at all. At least it's not Zone Alarm which "will" create issues.
If you search their forums , you will see it is definitely an issue on XP , especially when Chrome is installed and the workaround of disabling the helper service is the only thing that fixes it. The computer boots noticeably slower to your desktop picture and then it takes about another two minutes for the taskbar to show up and the icons take about another minute.
I have also discovered two other issues. If the Firewall component is enabled, it causes unacceptable stuttering in World of Warcraft. If you disable the Firewall, the game runs smoothly. The second issue is that if you completely shut down OA from the system tray icon by choosing "Close and shutdown", you can not restart the program. Only a reboot starts it back up again. This may be a result of disabling the helper service however.
I had none of these issues with the Comodo Firewall but it isn't as user friendly in it's setup or use.