why do some of my friends not appear as online when are standing right there

[Keebler58]

Firestorm 4.6.9 (42974) Dec 12 2014 12:47:58 (Firestorm-Releasex64) with OpenSimulator support
Release Notes

CPU: Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz (3392.16 MHz)
Memory: 8142 MB
OS Version: Microsoft Windows 8.1 64-bit  (Build 9600)
Graphics Card Vendor: NVIDIA Corporation
Graphics Card: GeForce GTX 645/PCIe/SSE2

Windows Graphics Driver Version: 9.18.0013.4448
OpenGL Version: 4.4.0 NVIDIA 344.48

RestrainedLove API: (disabled)
libcurl Version: libcurl/7.24.0 OpenSSL/1.0.1i zlib/1.2.6 c-ares/1.10.0
J2C Decoder Version: KDU v7.5
Audio Driver Version: FMOD Ex 4.44.41
Qt Webkit Version: 4.7.1 (version number hard-coded)
Voice Server Version: Not Connected
Settings mode: Firestorm
Viewer Skin: Firestorm (Grey)
Font Used: Deja Vu (96)
Draw distance: 128
Bandwidth: 1000
LOD factor: 2
Render quality: Medium-High (4/7)
Advanced Lighting Model: No
Texture memory: 512 MB (1)
VFS (cache) creation time (UTC): unknown
Built with MSVC version 1600

Also,

Ping Sim = between 95 and 115

Packet loss = 0%

Time Dilation = 0.994

Physics FPS = bounces between 39.7 at the lowest to 45.0

[Freya Mokusei]

Firstly there's an option to "hide online status", either world-wide or one-to-one. It's possible your friends are using these options - the purpose of doing so doesn't really matter.

Secondly the Friends system has plenty of bugs - especially if you're on a slow or limited connection - online status may be managed poorly. Though this is usually less of an issue if they're on the same simulator.

[Nalates Urriah]

Freya Mokusei provided a good answer.

In general the problem is caused by a poor connection. If you want to check your connection see: http://blog.nalates.net/2011/10/26/troubleshoot-your-sl-connection/

Also, when you ask a tech question include information about your computer and viewer. If the viewer will at least show the login screen, get the info from the viewer's Help-About... and paste that into your post with your question. Help->About... provides all the version numbers we need.  To add your info to an existing question use OPTIONS->EDIT. It’s in the upper right of your post.