Is it normal to ask to see the entire manuscript (not just the abstract) before accepting a peer-review invitation? I apologize if this question has been asked before. I received a peer-review invitation from a journal to review a paper. In the email there is just the author's name and the title of the article and an abstract. I should just tell them if I accept to review the paper or not by clicking on corresponding links. 

Is it normal to ask the journal to send the entire paper before accepting to review it? Isn't this request odd? I am potentially interested to review the paper (from the abstract, I guess I am familiar with the methods), but I would like to see the content to be sure if the methods used in the paper aren't beyond my knowledge and to check if I have enough time to review the paper (e.g., to avoid a surprise manuscript of > 150 pages!) If that matters, the subject is mathematics.
It is rather common in mathematics to have access to the full paper before deciding to review (it is attached or a link is provided). You could basically use what you wrote here as the basis for your reply. I specifically mean the phrase:


  I am potentially interested to review the paper, but I would like to see the content to be sure if the methods used in the paper aren't beyond my knowledge. 


I would just ask for the full paper with this reasoning. 

Only make sure to decide whether you are willing to review in a timely manner after you received the full paper.