One of my favourite Firefox plugins is It's All Text! which allows you to use an external editor to edit text areas in a browser page.
One of my favourite text editor (up there with UltraEdit) is vim and gvim. I wanted to use "It's All Text!" with gvim. It is easy enough to point the plugin at the gvim executable, but this meant each time I used the plugin, it would open a new gvim instance.
For Windows, this is the workaround I found to make sure "It's All Text!" would always open in the same gvim instance - opening a new tab each time. Create a cmd file:
@echo off "C:\Program Files\Vim\vim72\gvim.exe" --remote-tab-silent %1
Then point "It's all Text" to that batch file instead, e.g. C:\Documents and Settings\rbram\My Documents\Tools\Windows\editFileInExistingVim.cmd