user37: Every time I open the Tools menu, the IDE freezes for a few seconds. Why is that? It happens on both of my computers, and nothing I do makes a difference in how long it takes. I've tried restarting the IDE, unplugging my Uno, and many other things, but nothing helps.
I'm on windows, running IDE version 1.0.2.

user6254: I was having the same problem under Windows 7 x64 and had already removed all com ports and unknown devices as suggested above. For me, the solution was to rename "ListComPorts.exe" in the hardware\tools subfolder to "ListComPorts.exe.xxx" - this prevents the Arduino IDE from using this file and appearently it reverts to using the internal COM port detection mechanism (using DEVICE_ARRIVAL/DEVICE_REMOVAL messages??) . The tool menu now opens immediately every time.

user27: It's an RXTX issue. RXTX is the native serial library used to make the IDE talk to the boards.
On some Windows installation, with some Bluetooth things (both dongles or integrated), when enumerating serial devices, these dongles scan the air for remote serial devices. Hence, the IDE stays stuck, waiting for RXTX serial device enumeration to end. This issue has been acknowledged a lot of times, see for example #1375, #532, #200 and #143
As far as I understand, this issue does not affect linux or mac because of the different way the scan occurs. On linux it's a plain filtered file listing of /dev. Similarly it's on mac. On windows, it uses native API calls.
Some fixes are available in the 1.5 series but I suggest switching to the latest 1.5.6 release as RXTX was replaced by JSSC, a more modern and simpler library.

user275: Frederico Fissore already pointed out that this delay is due to the serial libraries. From a functional perspective: The Arduino IDE tries to enumerate all available COM ports which simply takes some time.
Quote from the official troubleshooting guide:

Why does do the Arduino software and the Tools menu take a long time to open (on Windows)?
If the Arduino software takes a long time to start up and appears to freeze when you try to open the Tools menu, there by a conflict with another device on your system. The Arduino software, on startup and when you open the Tools menu, tries to get a list of all the COM ports on your computer. It's possible that a COM port created by one of the devices on your computer slows down this process. Take a look in the Device Manager. Try disabling the devices that provide COM ports (e.g. Bluetooth devices).


37: <p>Every time I open the <code>Tools</code> menu, the IDE freezes for a few seconds. Why is that? It happens on both of my computers, and nothing I do makes a difference in how long it takes. I've tried restarting the IDE, unplugging my Uno, and many other things, but nothing helps.</p>

<p>I'm on windows, running IDE version 1.0.2.</p>
 6254: <p>I was having the same problem under Windows 7 x64 and had already removed all com ports and unknown devices as suggested above. For me, the solution was to rename "ListComPorts.exe" in the <strong>hardware\tools</strong> subfolder to "ListComPorts.exe.xxx" - this prevents the Arduino IDE from using this file and appearently it reverts to using the internal COM port detection mechanism (using DEVICE_ARRIVAL/DEVICE_REMOVAL messages??) . The tool menu now opens immediately every time.</p>
 27: <p>It's an RXTX issue. RXTX is the native serial library used to make the IDE talk to the boards.</p>

<p>On some Windows installation, with some Bluetooth things (both dongles or integrated), when enumerating serial devices, these dongles scan the air for remote serial devices. Hence, the IDE stays stuck, waiting for RXTX serial device enumeration to end. This issue has been acknowledged a lot of times, see for example <a href="https://github.com/arduino/Arduino/issues/1375">#1375</a>, <a href="https://github.com/arduino/Arduino/issues/532">#532</a>, <a href="https://github.com/arduino/Arduino/issues/200">#200</a> and <a href="https://github.com/arduino/Arduino/issues/143">#143</a></p>

<p>As far as I understand, this issue does not affect linux or mac because of the different way the scan occurs. On linux it's a plain filtered file listing of <code>/dev</code>. Similarly it's on mac. On windows, it uses native API calls.</p>

<p>Some fixes are available in the 1.5 series but I suggest switching to the latest <a href="http://arduino.cc/en/Main/Software#toc3">1.5.6 release</a> as RXTX was replaced by <a href="https://code.google.com/p/java-simple-serial-connector/">JSSC</a>, a more modern and simpler library.</p>
 275: <p>Frederico Fissore already pointed out that this delay is due to the serial libraries. From a functional perspective: The Arduino IDE tries to enumerate all available COM ports which simply takes some time.</p>
<p>Quote from the official <a href="http://arduino.cc/de/Guide/Troubleshooting#toc14" rel="noreferrer">troubleshooting guide</a>:</p>
<blockquote>
<p><strong>Why does do the Arduino software and the Tools menu take a long time to open (on Windows)?</strong></p>
<p>If the Arduino software takes a long time to start up and appears to freeze when you try to open the Tools menu, there by a conflict with another device on your system. The Arduino software, on startup and when you open the Tools menu, tries to get a list of all the COM ports on your computer. It's possible that a COM port created by one of the devices on your computer slows down this process. Take a look in the Device Manager. Try disabling the devices that provide COM ports (e.g. Bluetooth devices).</p>
</blockquote>
