chore(firefox): update cheatsheet with logging instructions (#1609)

browser_patches/firefox/cheatsheet.md

@@ -13,3 +13,16 @@ In native code use
 ```c++
 nsTraceRefcnt::WalkTheStack(stderr);
 ```
+
+If the stack trace is still mangled `cat` it to `tools/rb/fix_linux_stack.py`
+
+#### [Logging](https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Gecko_Logging)
+
+```bash
+MOZ_LOG=nsHttp:5
+```
+Module name is a string passed to the `mozilla::LazyLogModule` of the corresponding component, e.g.:
+
+```c++
+LazyLogModule gHttpLog("nsHttp");
+```