Chaos over, Internet Download Manager developer team seems to have finally hosted their extension, IDM Integration Module in the Chrome Web Store. So you no longer need to use developer mode to install their extension in stable and beta channels.
Update: IDM has removed their extension from the web store, we don’t know the reason for this? And now, you’ve to fall back to manually installing IDM Chrome Extension and it is still working.
UPDATE September 12, 2015: Extension is back on the Store.
Installing IDM Integration module in Chrome from Web Store
1. After installing IDM on your computer, visit this link in Chrome browser.
2. Click ‘Free’ and click on ‘Add’ button to install it.
If you don’t know: Google has made their policy tougher which means the Chrome browser strictly won’t allow extension installs outside Web Store, in case of stable channel Chrome 33, which soon to release, they’ve extended the deadline for hosting of extensions in online Store till May 1, after that, if you’ve their extension installed from other sources, it will be disabled and can’t be enabled by user like before.
Note: From onwards, always install IDM extension from the Chrome Web Store.