fix: potential race condition in prefs writing

WriteStream.write is asynchronous.  It is possible for write to not complete before Firefox is launched.
Use fs.writeFileSync instead.
Add aurora and nightly in the readme.
Disable popup blocking in browser profile

Launcher currently fails to run browser, as karma treats a new browser window as a popup. We need to disable dom.disable_open_during_load property in FF profile to make it run fine.
Merge pull request #11 from kud/master

Add aurora and nightly in the readme.
Merge pull request #14 from andrei-khveras/master

Disable popup blocking in browser profile
feat: disable "script not responding" dialog

Closes #7
Merge pull request #10 from bitwiseman/master

fix: potential race condition in prefs writing
fix: handle Firefox location on Windows

Currently the task assumes Firefox is located under process.env.PROGRAMFILES
directory. This is not true, as Firefox, being 32-bit on Windows, is located
in process.env["PROGRAMFILES(X86)"]. This commit adds a fallback to the second path,
being forward-compatible in case 64-bit Firefox gets released for Windows.
feat: Added ability to set custom preferences in firefox