How to extract omni.ja of Firefox

omni.ja can't be opened with the latest stable version of 7-zip 9.20,
but it can be opened with the latest unstable version of 7-zip 9.32.

Extract omni.ja to omni folder with 7-zip 9.32, ignore the errors during extracting.

After editing files in omni folder, go to omni folder, press Ctrl+A to select all files and folders, right click the files and folders you selected, go to 7-Zip menu and click Add to "omni.zip", rename omni.zip to omni.ja. Now you can replace the original omni.ja from Firefox with your modified omni.ja.

Note: omni.ja will be overwritten everytime Firefox is automatically updated to a new version, in other words, you must remodify omni.ja after Firefox is automatically updated to a new version if necessary.