CLI: Actual locally tested fix to race condition

Sorry for making new releases like this. It's that the live Browsh
services will only pull in officially released versions. But also that
this bug could affect a lot of people installing Browsh themselves.

interfacer/src/browsh/firefox.go

@@ -8,6 +8,7 @@ import (
 	"net"
 	"os"
 	"os/exec"
+	"path"
 	"regexp"
 	"runtime"
 	"strings"
@@ -230,12 +231,10 @@ func installWebextension() {
 	if err != nil {
 		Shutdown(err)
 	}
-	file, err := ioutil.TempFile(os.TempDir(), "browsh-webext-addon")
-	ioutil.WriteFile(file.Name(), []byte(data), 0644)
-	args := map[string]interface{}{"path": file.Name()}
+	path := path.Join(os.TempDir(), "browsh-webext-addon")
+	ioutil.WriteFile(path, []byte(data), 0644)
+	args := map[string]interface{}{"path": path}
 	sendFirefoxCommand("Addon:Install", args)
-	time.Sleep(100 * time.Millisecond)
-	defer os.Remove(file.Name())
 }
 
 // Set a Firefox preference as you would in `about:config`

interfacer/src/browsh/version.go

@@ -1,3 +1,3 @@
 package browsh
 
-var browshVersion = "1.6.3"
+var browshVersion = "1.6.4"