I want to achieve the function of a web offline, which is able to save some data, including image to the local, such as Internet access to the data update to the server database,

Search with indexedDB looks suitable, stored unlimited amount of data,

My question is
1. I tried put data into the chrome with indexeddb, but different browsers, such as firefox doesn't insert data in chrome, the reverse is also true, I see two browser save data are respectively in different directories, if it is with indexeddb can only be one and the same browser to access their own data, this seems very unreasonable

2. I emptied the inside of the chrome history information, such as cache content, after the data exist with indexeddb, so use with indexeddb realize my offline program, it seems that also not line, if after clear the cache, with indexeddb also can lose?

Is there any great god to give directions