You may want to use this to have a stable cross platform way of doing:
```
const tmpDir = require("sdk/system").pathFor("TmpD");
const file = require("sdk/io/file");
let log_path = file.join(tmpDir, "adb.log");
```
https://addons.mozilla.org/en-US/developers/docs/sdk/latest/modules/sdk/system.html#pathFor%28id%29