If you are asking about an address generated at Bittrex, then no, it doesn't change at all and it will be valid unless you login next time...
If you generate it, you can switch your tabs without any worries of losing that address, it will be valid unless you send your coins, as I guess that once you send coins to Bittrex, they will change it after the confirmations it will get...
Thank your for your help. So then I shouldn't have any problem. I'll do a test right now with a fraction of Ethereum
![Smiley](https://bitcointalk.org/Smileys/default/smiley.gif)
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Definitely not a problem at all, but remember, don't send another deposit to same address before checking it on the exchange...
You can go ahead for your first transaction without worrying about address being changed or invalid...